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How to do Business and Economics with a TI-89 Titanium

This page covers supply, demand, equilibrium point, marginal average cost, marginal cost and "next Item" cost, maximum profit, linear
programming, cost minimization, complementary/substitute product determination, and much more.
INDEX:

To facilitate lookup, the instructions are divided into the following categories:
I.  Supply, Demand, and Costs -  Equilibrium point; Marginal average cost;  Marginal cost and “Next Item”
cost; Maximum Profit;
Price, Revenue, and Quantity at given demand; determining price-demand function
from given data,

II.  Miscellaneous - Harmonic mean, Geometric mean, Mean of grouped data, How long to double interest, Leontief
input-Output problem,
III.  Linear Programming - Graphical Method; Graphing Using the Inequality APP, Simplex Method,
IV.  Calculus Applications - Determining functions with the calculator integration and differentiation functions, Cost,
Average Cost, Revenue, Demand, Marginal Cost, Average-Cost Minimization, Cost minimization,
Complementary/Substitute
Product Determination,
Equality of Marginal Product of Labor and Capital, Consumers' surplus, Suppliers' surplus,
I
MPORTANT NOTICE:  This page is being converted from TI-83 Plus to TI-89 Titanium.  Only the subsections displayed in bold type
in the index are suitable for the TI-89 Titanium.

IRELEASE DATE:  Not Released     DATE LAST REVISED:
© 2003 Frank Kizer   NOTE:  See copy restrictions and printing hints at the end of this document.

General:  Some of these problems can be solved more easily with a little calculus and some manipulations with paper
and pencil.  Nevertheless, I have included some rather simple problems as examples of how a graphing calculator
can be used.

I.  Supply, Demand, Costs and Related Items:

1. Equilibrium Point:
A certain produce has a demand function p = -2x² +80 and a supply function of p= 15x +25.  If x
represents the demand quantity in thousands and p the unit price in dollars, find the
equilibrium quantity and price.
a)  Highlight the Y= icon and press ENTER.  Enter right side of the demand equation opposite Y1 and the supply equation opposite Y2 .   Use the carat key, ^, to indicate and exponent.
b)  Press F2, scroll down to  A (ZoomFit) and press ENTER to get the graphs on the screen.
c)  Press F5 and select 5: Intersection.  Move the cursor off the intersection point a bit and press ENTER.
d)  Press either the up or down arrow as appropriate to move the cursor to the other curve.   Press ENTER.
e)  At the prompt Lower bound, move the cursor along the linear curve to a short distance before the intersection and press ENTER.  Move the cursor above the intersection point and press ENTER.
f)  The equilibrium point price, yc= 67.45, and equilibrium quantity, xc=2.69699, will be displayed.  Multiply the x-value by
1000 to get 2689.99 or 2690 rounded to the nearest whole number.

2.  Marginal Average Cost:

The cost function for manufacturing a certain household item is c(x) = 5000+2x.  Find the
marginal average cost for 500 units.
Preliminary:
The average cost function is c(x)/c = (5000+2x)/x.
a)  Enter (5000+2x)/x opposite Y1=.
b)  Set Xmin=0, Xmax=550, Ymin=0, and Ymax=150 and press GRAPH.
c)  Press F5, move the cursor to derivatives and press ENTER twice.
d)  Enter 500 and press ENTER. The value -0.02 will be displayed.

3.  Marginal Cost and “Next Item” Cost :

The cost of a certain product is given by c=700+0.03x +.0002x² .  Compare the marginal cost and
the “next item” cost at 150 units.
a)  Go to the Y= screen by pressing ♦, Y= (the F1 key) and enter  700+0.03x +.0002x²  opposite Y1 .    Press F2, move the cursor to
ZoomFit and press ENTER.
b)  Press F5, move the cursor to derivatives and press ENTER twice.
c)  On the screen that appears, enter 150 and press ENTER to get dy/cy=.09 for the marginal
cost.

Now, find the cost of item 151.
a)  Press 2ND, CALC, ENTER, for Value.
b)  On the same graph press F5, press ENTER for Value,  enter 150 and press ENTER to get 709.
c)  Press F5, press ENTER for Value,  enter 151 and press ENTER to get 709.09.
d) This gives 709.902-709=0.0902 for the actual cost of manufacturing item 151.

4.  Finding Maximum Profit:

The demand of a certain product is represented by p=40/√q and the cost of producing q items
is given by c= .04x +400.  Find the number of items that gives maximum profit and the price
that yields maximum profit.
We know, of course, that the maximum profit occurs when the cost of producing another item
(approximated by the marginal cost)) is equal to the revenue and on that item (marginal
revenue).
P=R-C
= xp(x) - C(x)

=x(40/√(x)) –(0.4x +400)
=40√(x) –0.4x -400
a) Go to the Y= screen by pressing ♦, Y= (the F1 key).
b)  Enter 40√(x) –0.4x -400 opposite Y1
c)  Press ♦, WINDOW and set x-min=0, Xmax=5000, Ymin=300, and Ymax=700.  Press ♦, GRAPH.
d)  Press F5, 4, to get the "lower bound" prompt..
d)  Move the cursor somewhat to the left of the maximum of the curve and press ENTER.
Move the cursor somewhat to the right of the maximum of the curve and press ENTER.
e)   The terms displayed will indicate x=2500 and y=600.  So, the maximum profit occurs at 2500
items and the maximum profit is \$600.
f)    To get the price equation, do the following calculation:
p= 40/√x
p= 40/√2500
p=0.80

5.  Price at a Given Demand:

The relation between price, p,  and quantity demanded, q, is given by the equation
p² =12000-2x.  Find the price when the demand is 3900 and 4100.
First solve for the price as a function of x.
p² =12000-2x
p=√(12000-2x)
Ex 1:

a)   Press ♦, Y= and enter  √(12000-2x) opposite Y1
b)  Press♦, WINDOW and set Xmin=0, Xmax=6500, Ymin=0, and Ymax=110.  Press GRAPH to
display the graph.
c)  Press F5, ENTER and enter 3900.
d)  Press ENTER and the answer 64.807… will be displayed.
e)  After you have recorded the last  answer, press F5, ENTER; then  enter 4100 and press ENTER to get 61.644…
Ex 2:

For the price-demand relation of Ex. 1 above, find the maximum revenue and the quantity
that gives the maximum revenue.

a)  Enter  x√(12000-2x),  the expression for R(x), opposite Y2.
b)  Move the cursor to highlight the expression opposite Y1 and press F4 to disable the graph for
revenue.  Press F2, move the cursor to ZoomFit and press ENTER to display the graph.
c)  Press F5, CALC 4(maximum).
d)  When the graph appears, move the cursor somewhat to the left of the peak and
press ENTER.  Move the cursor somewhat to the right of the peak and press
ENTER.
e)  A quantity of x=4000 and revenue of y=252982.21 will be displayed.
Ex. 3:

Find the price at maximum revenue.
a)  Disable Y2 by moving the cursor to the the expression opposite Y2  and pressing F4.  Enable Y1 by moving the cursor
to highlight the expression  opposite Y1 and pressing F4.
b)  Press F2, move the cursor to A:(ZoomFit) to display the graph.
c)  Press F5, ENTER.
d)  From the graph screen that appears, enter 4000 and press ENTER.  The price
63.245… will be displayed.

6.  Price-Demand Function from Given Data:
I will give the method for doing this problem totally with the calculator; then I will give a method for doing
detailed calculations to find the constants “a” and “b” in the best-fit equation

A company determines the price-demand relationship of one of its products is related as given in the table
below.  Determine the price-demand function,  the price at 8000 units, the maximum revenue and the value at
at which maximum revenue occurs.

TABLE 1:  Price-Demand Values

 Quantity (x 103 ) Price 1000 72 4000 63 9000 48 14000 33 20000 15

First you need to get your data in lists.  You can do that from the home  screen, but if you have any
significant amount of data, it's much easier to enter it into list tables.  See the note at the beginning of
this document for instructions on clearing lists if you want to clear your lists before data entry.
Here's how to enter data:
a)
Press APPS, S,  highlight the Stats/List icon and press ENTER.   If the tabulated lists do not appear, press
ENTER again.
b)  Enter
the numbers for the independent variable, x-values,  in list1 and the corresponding values in list2.
c)   From the list screen, press F4, 3 and choose the regression equation of your choice, for example 2, for
LinReg (ax+b).  Press the number for your selection.
d)  On the dialog box that appears, enter list1 opposite "x" and list2 opposite "y."  Enter list1 by pressing
2ND, VAR-LINK, l (L, not 1), highlight list1 and press ENTER.  Move the cursor down opposite "y" and
repeat the steps to enter list2 there.
e)  If you are planning to graph the equation,  the box opposite "Store RegEq to"
should have  y1(x) in it.  If not, press the right arrow; then press ENTER.  Enter 1 for Freq. if in is not already
there. .
f)
Press ENTER and the values for "a," -0.003, and "b, "  75, will be displayed along with other results. So, the
demand function is P= -0.003X+75.
Graphing the Regression Equation to Get the Price At 8000 Units:

a)  If you want to graph the regression equation, press
♦, Y=.  That will take you to the Y= screen.
b)  Clear or deselect all of the entries except Y1 and check Y1by pressing F4 if it's not already checked.
c)
Press♦,  WINDOW and set Xmin=0, Xmax=8500, andYmin=0.  Press F2, move the cursor to (ZoomFit) and press ENTER.
The  graph will be displayed.
Now, find the maximum revenue.
a)  While still on the same graph, pressF5, 4 (maximum) and the "Left Bound" prompt will be  displayed.
f)  Move the cursor somewhat to the left of the peak of the graph and press ENTER.
Move the cursor to slightly to the right of the peak and press ENTER again.   X=12500 and Y=468750 will be displayed.
These are the quantity at which maximum revenue occurs and the maximum revenue at that quantity.

The material between this point and Section IV is under construction and cannot be used for the TI-89 Titanium.
The first few procedures in Section IV have been redone for the TI-89 Titanium.

Detailed Calculations:

Since many teachers use the detailed calculations as an instructional  method, I will now go through a fairly detailed
calculation of the constants “a” and “b.”  Assume that we have the  x- and y-values as listed in the table in the first part
of this problem.

 L1 Quantity (x) (x 103 ) L2   Price (y) L3   x² L4 xy 1000 72 1E6 72000 4000 63 1.6E7 252000 9000 48 8.1E7 432000 14000 33 1.96E8 462000 20000 15 4E8 300000 ∑xi = 48000 ∑yi= 231 ∑ xi² = 6.94E8 ∑xiyi=1.52E6

We will now calculate the values for x² and xy which have already been entered in the table on this page.
a)  Press APPS, S,  highlight the Stats/List icon and press ENTER.   If the tabulated lists do not appear, press
ENTER again.
b)  Enter
the numbers for the independent variable, x-values,  in list1 and the corresponding values in list2.

b)   Highlight the name, list3.  Press 2nd, ALPHA and type "list."  Press ALPHA to disable the letter
function and enter 1.  now enter ^, 2. Press ENTER and the numbers will be stored in list3 .
c)
Highlight the name for  list4.  Press 2nd, ALPHA and type "list."  Press ALPHA to disable the letter
function and enter 1.  Now enter "llist1, *, list2" using the method indicated above.  . Press ENTER and the numbers
will be stored in list4 .  Note that you can save yourself the drudgery of typing the list names by pressing 2nd, VAR-LINK
(the minus key), enter the letter "L," and select the list you want and press ENTER.

Now, solve the system of equations indicated as follows:
∑x i)b +(∑xi²)m =  ∑xiyi

nb   +(∑x i)m =  ∑yi
In these equations, “m” is the slope and “b” is the y-intercept.  Those may be designated by such constants
as "a" and "b" in some texts.
In terms of our lists in the table above, these equations can be written as a matrix as follows:
∑list1 +(∑list3
=  ∑list4

n   +(∑list2 =  ∑list3
Enter the Coefficients into the Matrix:
a)  Press APPS, press "D" for Data/Matrix and press ENTER.
b)  Create a 2x3 matrix by pressing 2nd, F6 ( the F1 key); then perss 6 for "Resize Matrix."  Press ENTER and enter
2 for rows and 3 for columns in the dialog box that appears.   Then press 2nd QUIT to leave the matrix editor.
We are now going to sum the lists, enter the numbers in the matrix, and display the numbers all in a
series of repetitive steps.
c) Press 2nd, APPS to take you back to the list screen.
d)  Press 2nd, L1, STO, MATRIX, ENTER, (, 1, 1, ).  You should now have sum(L1 -->[A](1,1) on the home
screen.
e)  Press ENTER and the number will be stored in the first element of matrix [A] and will be displayed on the
home screen.
f)  Press 2nd, ENTRY to recall the above expression.  Place the cursor on L1 and press 2nd, L3; then move the cursor
to the matrix name and change the element so that you have [A](1,2).  Press ENTER and the actions described for
the first element will be performed.

g)  Press 2nd, ENTRY to recall the above expression.  Place the cursor on L3 and press 2nd, L4; then move the cursor
to the matrix name and change the element so that you have [A](1,3).  Press ENTER and the actions described for
the first element will be performed.

g)  Press 2nd, ENTRY to recall the above expression.  Place the cursor on L4 and press 2nd, L1; then move the cursor
to the matrix name and change the element so that you have [A](2, 2). You will notice that we skipped [A](2,1) for the
present.   Press ENTER and the actions described for the first element will be performed.
h)  Press 2nd, ENTRY to recall the above expression.  Place the cursor L1 and press 2nd, L2; then move the cursor
to the matrix name and change the element so that you have [A](2,3). Press ENTER and the actions described for the
first element will be performed.
i) Press 2nd, ENTRY, place the cursor on sum( and press DEL; then move the cursor to L2 and press 5, the number for "n"
in this particular problem.  (If " n" is a two-digit number just start the entry without deleting the sum(. Now,
change the matrix designation to [A](2,1]. Press ENTER to store "n" in the matrix.
Now, we are going to solve the equations for "a" and "b."
d) Press 2nd, MATRIX, move the cursor over to math,  and then select rref( and press ENTER.
e) Press 2nd, MATRIX and then ENTER if you have entered your numbers in [A], otherwise select the proper matrix.
and press ENTER.  You should now have rref([A] on the screen.
f )  Press ENTER to get the answer.  The first row will be "b" and the second will be "a."  You'll get almost the same answer
as with all of the arithmetic.
COMMENT:  The matrix method may seem like a formidable number of steps, but is saves many, many individual arithmetic
steps.

II.  Miscellaneous:
1. Harmonic mean:
Suppose that an investor has \$1000 to invest each month and he pays \$8.00, \$8.50, \$9.00, \$9.50, \$10.00, and \$10.50 for the
for the first six months.  What is his average cost per share?
a)  Press STAT, ENTER to go to the lists and enter the data in list L1.
b) Place the cursor on the name for L2 and enter 1, ÷, 2nd, L1, so that you have 1/L1..  Press ENTER and the reciprocals will
be displayed

c) Press 2nd, QUIT to leave the list editor and press 1, ÷, (.  Press 2nd, LIST, move the cursor to MATH, and press 5 for sum(.
d) Press 2nd, L2, ), ÷, 6, ).  You should now have 1/(sum(L2)/6)
e) Press ENTER and \$9.1706....will be displayed as opposed to the arithmetic mean of \$9.25.

2. Geometric mean:
Suppose that during the past five years you has 75%, 10%, 30%, 20%, and -60% returns on your investment.  What would be
your average return for the five-year period?  You can enter ((1.75*1.1*1.3*1.2*.4)^(1/5))-1, but if you have a more complex
problem or you don't like entering number, you can do it as follows:
a)  Press STAT, ENTER and enter the percentages in list L1.
b)  Move the cursor to highlight the name for L2 and press 2nd, L1, ÷, 100, +, 1.  So that you have L1/100 +1 and press ENTER.
c) Move the cursor to the first blank space in L2 and press (,; l then press 2nd, LIST.  Move the cursor to MATH and press 6 to
paste prod( to the bottom of the list screen.
d) Press 2nd, L2, ), ^, (1, ÷, 2nd, 5)-, 1.  You should now have (prod(L2))^(1/5) -1 at the bottom of the list screen.
e) Press ENTER and you will get .03734 or 3.734% rather than 15% for the arithmetic mean.

3)  Median of Grouped data:

Consider the following table.

 Age 5-14 15-24 25-34 35-44 45-54 Midpoint 9.5 19.5 29.5 39.5 49.5 Freq (People) 750 2005 1950 195 100

a)  To find the median class, enter the midpoints in L1 and the frequencies in L2 .
b)  Press STAT, move the cursor to highlight CALC and press ENTER.  1-Var Stats will be displayed on the home screen.
c)  If the data are in lists L1 and L2 just press ENTER.  If they are in other lists, you must enter the lists.  For example,
press 2ND, L2, comma, 2ND, L3 and then press ENTER
d)  Press ENTER and scroll down to Med=19.5.  That is the median of the class 15-
24. So 15-24 is the median class.
e)  Enter the appropriate data into the following formula:
Median = L + I *(N/2 - F)/f
Where
L = lower boundary of the interval containing the median.
I = width of the interval containing the median.
N = total number of respondents.
F = cumulative frequency of those below the median class.
f = number of cases in the median class.
f)  When you are finished entering, you should have this:
14.5+10(5000/2-750)/2005
g)  Press ENTER and you should get 23.228… Notice that the answer is different form
the value of 19.5 given by the calculator. That value of 19.5 was chosen by merely finding the  midpoint
of the median class.

4.  How Long to Double Interest:
Although this could be found using the Finance Application, here's a quick way to do it.
An investment has a 7% interest compounded annually.  How long will it take for the value
to double?
Preliminaries:   From the equation A=P(1+r/n)nt , we have 2P=P(1+0.07)t .  Cancel "P" and we have
2=1.07t , or 2=1.07x for the calculator.
a)  Press Y= and enter 2 opposite Y1; then enter 1.07^x opposite Y2.
b)  Press WINDOW and set Xmin=0, Xmax=15, Ymin=0 and Ymax=3. Press GRAPH.
c)  Press 2ND, CALC, 5 (for Intersect).
d)  From the graph screen that appears, press ENTER, ENTER; then move the cursor near the intersection
of the two lines and press ENTER again.  The answer of 10.24 years will be displayed.
Note that you can find other factors such as triple or quadruple by merely changing Y1 to 3 or 4.

5.  Leonfief Input-Output Problem:

Suppose that an economy consist of the sectors of food, clothing, and shelter.  In that economy, producing one unit of food
requires 0.4 units of food, 0.2 unit of clothing, and 0.2 units of shelter Producing one unit of clothing requires 0.1 units of
food, 0.2 units of clothing, and 0.3 units of shelter.  Producing one unit of shelter requires 0.3 units of food, 0.1 unit of clothing,
and 0.1 unit of shelter.  The economic demands are \$100-million of food, \$30-million of clothing and \$250-million of shelter.
Find the level of production needed to meet  these demands.
We can write the following input-output matrix:

 F S C F 0.4 0.2 0.2 C 0.1 0.2 0.3 S 0.3 0.1 0.1

And the following for the demand matrix:

 100 30 250

From the Leontief input-output model we have this:
X-AX =D
X=(1-A)-1 D
a)  Press 2ND, MATRIX, move the cursor  to EDIT and enter the input-output matrix in matrix [A].  Press 2ND, QUIT to
leave the matrix editor.
b)  Press 2ND, MATRIX, move the cursor  to EDIT and enter the demand matrix in matrix [B].  Press 2ND, QUIT to
leave the matrix editor.
Now, we want to enter the appropriate expression for (1-A)-1 D.
c)  Press 2ND, MATRIX, move the cursor to MATH and press 5(identity), 3, ), - (minus sign).
d)  Press 2ND, MATRIX, ENTER, ).  You should now have (identity(3)-[A]) on the home screen.
e)  Press x-1 , 2ND, MATRIX , 2(for matrix [B]), You should now have (identity(3)-[A])-1 [B] on the home screen.
f)  Press ENTER to get 396.34 for food, 252.22 for clothing, and 437.80 for shelter.  All are rounded to two decimal
places.

III.  Linear Programming:

1. Graphical Method:
Ex 1:
Suppose that we want to maximize the objective function with function and constraints defined
as follows:
z=2x+5y
3x+2y≤6
-x+2y≤ 4
x
≥0, y≥0
a)  First rewrite the inequalities in slope-intercept form:
y≤(-3/2)x +3
y≤x/2+2
b)  Press Y= and enter the expressions in Y1 and Y2.  If you wish, you can do the shading by moving the
cursor over to the left and pressing ENTER until you get the third-quadrant triangle for <, but I prefer to
just graph the equations.
c)  Press WINDOW and set the following: Xmin=0, Xmax=5, Ymin=0, Ymax=4.  Press GRAPH and the
graphs will be displayed.  You can read the points (0,2) and (2,0) from the graph, but we want to find
the point of intersection.
d)  To find the intersection point press 2ND, CALC, 5(Intersect), move the cursor back to about x=.7 and
press ENTER. Press ENTER, ENTER  after the cursor has moved to the other curve and x=.5, y=2.25
will be displayed.
f)  We now have the points (0,2), (.5, 2.25), and (2,0) that we want to plug into the objective function. You
could do this manually fairly easily, but there may be occasions when it is not done so easily by hand.
Do the calculations with the calculator as follows:
1)  Press 0, STO, X (use the [x,T,0,n] button for X), ALPHA, : (the decimal button), 2, STO, ALPHA, Y,
ALPHA, :,  2, X, +,  5, ALPHA, Y. You should now have 0
→X:2→Y:2X+5Y.
2)  Press ENTER and 10 will be diplayed.
3)  Now, press 2ND, ENTER and change the stored values of X and Y, so that you have the following:
.5→X:2.5→Y:2X+5Y.  Press ENTER and 13.5 will be displayed.
3)  Now, press 2ND, ENTER and change the stored values of X and Y, so that you have the following:
2→X:0→Y:2X+5Y.  Press ENTER and 4 will be displayed.
So, the point (.5, 2.25) maximizes the objective function.
Using the Inequalz APP:

2)  Graphical Linear Programming with the Inequalities Application:

Do the same problem as above, that is, find the maximum of the objective function z=2x +5y, subject to the following constraints:

3x+2y≤6
-x+2y≤ 4
x
≥0, y≥0

a)  First rewrite the inequalities in slope-intercept form:
y≤(-3/2)x +3
y≤x/2+2

b)  Enter the right side of those equations opposite Y1 and Y2 respectively and enter 0 opposite Y3.
c)  Set the WINDOW at Xmin = -1, Ymin=-1, Ymax= the largest value of "b" plus a few units, say 5 in
this problem.
Xmax is a bit more difficult to anticipate.  If there is an equality with a negative slope, I usually
make Xmax = 4/3*b/m, round it off to the next largest whole number and add a few units. You can
enter the arithmetic opposite Xmax. You might want to press GRAPH and see if all of the
corner points of the bounded region are on the screen.
Now we will enter the inequality signs.

a)  Move the cursor to the sign (either equal or inequality) after Y1.  If the inequality symbols do not
appear at the bottom of the screen, you will need to start the Inequality App.  Do that by pressing
APPS, move the cursor down to Inequal,  or Inequalz for the international version, and press
ENTER, ENTER.  The Y= editor screen should be displayed.
b)  Place the cursor on the equal sign opposite Y1 and press ALPHA, F3 (ZOOM).  The equal sign
should have been replaced by the inequality ≤.
c)  Do the same for Y2; then opposite Y3, press ALPHA, F5 (GRAPH).  The symbol ≥ should have
replaced the equal sign before the 0.
d)  Now, move the cursor up to the "X" in the upper left corner and press ENTER.  With the cursor on the
equal sign opposite X1, press ALPHA, F5 (GRAPH) to enter
;  then enter a zero after that symbol.
e)  Press GRAPH  to draw and shade the graphs.
f)  Press ALPHA, F1, 1 to define the feasible region.
If you only want to graph, you may stop here.
At this time we will find the x- and y-values of the corner points.  We will use a method to have the
calculator determine the corresponding values of the objective function.  If you prefer to determine
those values manually, just record them without pressing STO so that you can substitute them into
the objective function.
a)  Press ALPHA, F3 (ZOOM) and  x=.5, y=2.25 will  be displayed.  Record these values if you choose to evaluate the objective
function by hand.  Otherwise, press STO, ENTER.
b) Press the down arrow to move to the point x=2, y=0 and press STO, ENTER.  Note that different sequences of the cursor
keys may be needed to read the points.  It takes a little experimenting.
c)  Press the right arrow; then then down arrow to read the last point, x=0, y=2.
Having the calculator evaluate the objective function.

a)  Press STAT, ENTER, to bring up the lists with the stored data.

b)  First we will name the list after list INEQY.  We will name it OBJ.  Move the cursor to the name
block at the top of that list.  Press 2ND, ALPHA, O, B, J, ENTER.
Now, we will define the list OBJ.
c)  With the curosor on the list name, press ALPHA, " (the + key), 2, x(multiply), 2ND, LIST and scroll down to
INEQX and press ENTER.
d)  Press +, 5, x (multiply), 2ND, LIST, scroll to INEQY and press ENTER.  Press ALPHA, ".  You should now have
"2*└INEQX+5*└INEQY" at the bottom left of the screen after "OBJ=".  Press ENTER and the values
of the objective function for each set of coordinates will be displayed in the OBJ list.
Admittedly, this is a rather formidable list of steps, but after a little practice, it becomes quite easy.

2.  Application Using the Graphical Method:
Suppose a company manufactures two types of products Good and Better and it has two machines 1 and 2.  The
company will realize a profit of \$5 on each Good item  and \$4 on each Better item.  To manufacture a Good
item, 6 minutes are required on machine 1 and 5  minutes on machine 2. To manufacture a Better item,
9 minutes are required on machine 1 and 4 minutes on machine 2.  If 5 hours are available on machine 1 and
3 hours are available on machine 2, how many of each should be manufactured to make the most profit?
To facilitate graphing, let x = the number of good items and y the number of best items.  Then we want to
maximize the following profit function:
P=5x+4y
We can make a table for our constraints as follows:

 Machine G B Totals 1 6 9 300 2 5 4 180

So, we can write the following constraints:
6x+9y≤300
5x+4y≤180
x ≥ 0, y ≥0
a)  First rewrite the inequalities in slope-intercept form:
y≤-2/3x +300/9
y≤-5/4x+45
b)  Press Y= and enter the expressions in Y1 and Y2.  If you wish, you can do the shading by moving the
cursor over to the left and pressing ENTER until you get the third-quadrant triangle for <, but I prefer to
just graph the equations.
c)  Press WINDOW and set the following: Xmin=0, Xmax=50, Ymin=0, Ymax=45.  Press GRAPH and the
graphs will be displayed.
d)  To find the intersection point press 2ND, CALC, 5(Intersect),  ENTER, ENTER.   Move the cursor to the
approximate intersection and press ENTER again.  The values X=20, Y=20 will be displayed.
Now, we want to find the point where the feasible region intersects the x- and y-axes.
e)  Press 2ND, CALC, ENTER (for Value). The values x=0, y= 33.33.... will be displayed.
f)  Press 2ND, CALC, 2 (for zero) and make sure the equation -5/4x +45 is displayed at the top of the screen.
If it is not, press the up arrow of the cursor control.
f)  Move the cursor down until you are at about x=3 or so and press ENTER.  Move the cursor to some small
negative number and press ENTER again. Finally, move the cursor to about zero and press ENTER again.
The values X=36, Y=0 will be displayed
f)  We now have the points (0, 33.3 ), (20, 20), and (36,0) that we want to plug into the objective function. You
could do this manually fairly easily, but there may be occasions when it is not done so easily by hand.
Do the calculations with the calculator as follows:
1)  Press 0, STO, X (use the [x,T,0,n] button for X), ALPHA, : (the decimal button), 33, STO, ALPHA, Y,
ALPHA, :,  5, X, +,  4, ALPHA, Y. You should now have 0
→X:33→Y:5X+4Y.
2)  Press ENTER and 132 will be diplayed.
3)  Now, press 2ND, ENTER and change the stored values of X and Y, so that you have the following:
20→X:20→Y:5X+4Y.  Press ENTER and 180 will be displayed.
3)  Now, press 2ND, ENTER and change the stored values of X and Y, so that you have the following:
36→X:0→Y:5X+4Y.  Press ENTER and 144 will be displayed.
So, the point (20, 20) maximizes the objective function.

3. Simplex Method:

By far the simplest method for solving simplex problems is with a calculator program.  Later,
I'll give you a location on my Website where you can find programs to download.  However,
many students may not solve more than a half-dozen simplex problems in their college career, and some
professors will require doing simpler simplex problems by hand. So I will include a semi-automated method
to reduce the drudgery of arithmetic and to reduce errors.
Ex 1:
Suppose that we want to maximize the objective function with the function and constraints defined
as follows:
z=3x1+2x2+x3
2x1+ x2 +x3
≤150
2x1+2x2+8x3
200
2x1+3x2+x3
≤ 320
x
1≥0, x2≥0, x3
We introduce slack variables and have the following simplex tableau:

z=3x1+2x2+x3
x1+ x2 +x3
s1   s2   s3  |    .
2      1      1      1    0      0   |150
2      2      8      0    1      0   |
200
2     3    1     0  0     1   |
320
-3     -2     -1     0   0       0    |0
Now, we want to solve this simplex problem.  Using the Matrix operations, do that as follows:
a) Press 2ND, MATRIX, move the cursor to EDIT and press ENTER.
b) Change the dimensions to 4 x 7 and enter the values into the matrix.  Just enter the number and
press ENTER to do that.
c)  After you have completed entering the information, press 2ND, QUIT to go the home screen.
d)  Just as a precaution, let's store this in matrix [B] just so we won't have to re-enter everything
in case we make a mistake.  So, press 2ND, MATRIX, ENTER, 2ND, MATRIX, 2(B).  You should now
have [A]→[B] displayed on the screen.  Press  ENTER and the storing will take place and the matrix
will be displayed.
e) Now, we want to decide where to pivot.  Since -3 is the most negative number, select that column.
Now, divide each number in that column into the numbers at the end.  The first number gives
150/2=75, which is smaller that the other quotients.  So, we will pivot on that point.
Row Operations:
Now, we want to use matrix row operations to leave a 1 in the pivot location and zeros in all other
positions in that column.  The syntax of the Operation that we will use is as follows:
cc→M:c→A:c→R:*row+(M, [A], A,R)→[A],  where c is a character (number, minus sign, etc.) , M is the
row multiplier, A is the number of the row being multiplied, and R is the row being replaced.
Remember that the arrow indicates pressing the STO key, the colons are obtained by pressing
ALPHA and the decimal key, and *row+( is obtained by pressing 2ND, MATRIX, moving the
cursor to MATH, scroll down to *row+( and pressing ENTER.  The matrix symbol [A], must be
obtained by pressing 2ND, MATRIX, ENTER.
f)  Now, let's do row 2.  We will have the following on the home screen:
-1→M:1→A:2→R:*row+(M, [A], A,R)→[A].  Press ENTER and a zero will appear in the appropriate
cell with the other cells in row two modified accordingly.
g)  We want a zero in place of the 2 in row 3.  Press 2ND, ENTER and edit the number for R, so that the display
now reads as follows:   -1→M:1→A:3→R:*row+(M, [A], A,R)→[A].  This will set up the matrix operation
as follows: *row+(-1, [A], 1, 3)→[A].  Press ENTER and the changed matrix will be displayed.
h)  We want a zero in place of the -3 in row 4.  Press 2ND, ENTER and edit the numbers for M and R,
so that you have this:  3/2→M:1→A:4→R:*row+(M, [A], A,R)→[A].  This will set up the matrix operation
as follows: *row+(3/2, [A], 1, 4)→[A].   Press ENTER and the changed matrix will be displayed.
i)  We want to reduce the first number, 2 to 1.  Normally, we would use the multiply row function to
do that, but to reduce key strokes, we're going to do it another way.  So, press 2ND, ENTER and
edit the display so that it reads as follows: -1/2→M:1→A:1→R:*row+(M, [A], A,R)→[A].  Press
ENTER and the following will be displayed.
[[  1     .5      .5      .5    0    0    75]
[ 0       1      7       -1    1    0
50]
[0     2     0     -1  0     1  17]

[ 0     -.5     .5     1.5   0      0  225]]
Now, the pivot point will be on the 1 in column 2.
j)  We want a zero in place of the 2 in row 3 Column2..  Press 2ND, ENTER and edit the numbers for M,
and R, so that you have this:  -2→M:2→A:3→R:*row+(M, [A], A,R)→[A].  Press ENTER and the changed
matrix will be displayed

k)  We want a zero in place of the .5 in row 1, column2.  Press 2ND, ENTER and edit the numbers for M and R,
so that you have this:  -.5→M:2→A:1→R:*row+(M, [A], A,R)→[A].  Press ENTER and the changed
matrix will be displayed.
l)  We want a zero in place of the -.5 in row 4, column 2.  Press 2ND, ENTER and edit the numbers for M and R,
so that you have this:  .5→M:1→A:4→R:*row+(M, [A], A,R)→[A].  Press ENTER and the changed
matrix will be displayed.
Since there are no more negative numbers in the last row, the solution is now complete.  The solution
you should have is as follows:
[[  1        0      -3        1    -.5    0    50]
[ 0       1      7        -1      1    0
50]
[
0        0   -14     1    -2   1    70]
[ 0       0      4        1       0      0  250]]

3.  Simplex Method with a Calculator Program:

There are a number of program available on the Internet.  You can either use one of my programs or do a Google
search to find another source.   Here's the URL to go directly to my programs.
http://www.angelfire.com/pro/fkizer/ti_programs/tiprograms.htm
Notice that there are different program depending on the type simplex problems you want to solve.  My programs
are in text for manual entry and in .8XP format for download and entry by computer.  The instructions are included
with the programs.

IV.  Calculus Applications:
General:  Before we get into any solutions to detailed problems, let's do some calculus operations of a general nature
using the calculator.
1.  Given Marginal Cost Function, Find Cost and Average Cost Functions:
Suppose that we are given the marginal cost function dC/dx = 4x-10 and a fixed cost of \$30.  Find the Cost function and
average cost function.
a) Press HOME, F3, 2 for ∫(.
b) Enter 4x-10, x), so that you have
∫(4x-10,x).
c)  Press ENTER and the function 2x2 -10x will be displayed.  Add the fixed cost to get the cost function, 2x2 -10x+30.
d)  To get the average cost function, just divide that by x.  That is, C(x)/x = (2x2 -10x+30)/x.  You can simplify that if you
wish, but for graphing it's not really necessary.
From the cost function, find the cost of producing 1500 units:
a)  Highlight the cost function on the calculator and press F1, 5 to copy that function.
b)  Now press
♦, Y= ( the F1 key) place the cursor opposite y1, and press F1, 6 for Paste.  Add 30 to the expression at the bottom
of the screen, so that you now have
2x2 -10x+30.
c) Press ENTER to place the expression opposite y1.
d)  Press F2, scroll to SoomFit and press ENTER.  The graph will be displayed.

Now, we are ready to find the cost at 1500 units.

e)  Press F5, ENTER for Value.
f)  When the graph appears, enter 1500 and press ENTER.
g) The answer yc=4.48503E6 will be displayed.  That, of course, is \$4,485, 030.

2.  Given Marginal Revenue Function, Find Revenue and Demand Functions:
Suppose that we are given the marginal revenue function dR/dx = 50-14x-12x2 and we want to find the revenue and demand
functions.
Find the Revenue Function:
a) Press HOME, F3, 2 for ∫(.
b) Enter 50-14x-12x^2 , x), so that you have ∫(50-14x-12x^2 ,x).
c)  Press ENTER and the revenue function -4x3 -7x2 +50x will be displayed.
Find the Demand Function:-

a) The demand function is just R(x)/x. That is, (-4x3 -7x2 +50x)/x.  It's not worth the effort to put that in the calculator unless
you want to graph it.  At any rate, it's -4x2 -7x+50.
Of course, we could graph any of these using the above techniques if we wanted.
Material beyond this point is still under construction and cannot be used by the TI-89 Titanium.

3.  Cost, Average Cost, and Marginal Cost:
Suppose that a company estimates that the cost (in dollars) of producing x units of a certain product is given by
C(x) = 200+0.05x+0.0001x².
Cost of producing 500 units.
a)  Press Y= and enter the equation 200+.05x +.0002x². Use the [X,T,0,n] key to enter x and the x² key to
enter the exponent after entering x.
Press WINDOW and set Xmin at 450; then press ZOOM, 0 (ZoomFit) display the graph.
b)  Press 2ND, CALC, ENTER.
c)  From the displayed graph screen enter 500 opposite s and press ENTER.  The cost of 250 will be displayed.
Average cost of producing 500 units.
a)  Press Y= and change the entry so tha tit is as follows: (200+.05x +.0002x²)/x
Press WINDOW and set Xmin=450; then press ZOOM, 0(ZoomFit) to display the graph.
b)  Press 2ND, CALC, ENTER and enter 500 opposite x.
c)  Press ENTER and x=500, y=.5 will be displayed.  The average cost is \$0.50.
Marginal Cost for 500 Units:
a)  Change the equation back to the cost equation: 200 +.05x+ .0001x².
b)  From the graphing screen press, 2ND, CALC, 6(dy/dx).
c)  Enter 500 and press ENTER.  The equation dy/dx =.15 will be displayed.

4. Average-Cost Minimization:

Find the number of units that will minimize the average cost and the corresponding cost.
We want to find the point where C(x) = C'(x), so we'll need the first derivative: c'(x)=.05+.0002x.
a)  Enter (200+.005x+.0001x²)/x opposite Y1 and .05+.0002x opposite Y2.
b)  Set x-min = 450 and x-max = 200.  Press ZOON, 0(ZoomFit) to display the graphs.
Now find the intersection point.
c)  Press 2ND, Calc, 5 (intersect).
d)  From the graph screen, press ENTER, ENTER; then move the cursor approximately to the intersection
and press ENTER again.
e)  The numbers x=1414.21... and y=.332... will be displayed.  So, the number to minimize average cost
is approximately 1414 and the cost is approximately .332 dollars.

5.  Cost Minimization;
The cost C(x) of manufacturing x units of a produce is approximated by the following: C(x) =100+10/x+x²/100.
Find the number of units that should be manufactured to minimize cost.
a)  Press Y= and enter the equation 00+ 10/x + x²/100. Use the [X,T,0,n] key to enter x and the x² key to
enter the exponent after entering x.  Press WINDOW and set Xmin =0, Xmax=50, Ymin=90 and Ymax =140.
b)  Press 2ND, CALC, 3 (minimum), and move the cursor to the left of the minimum (about 5) and press ENTER.
Move the cursor to the right of the minimum (about 20) and press ENTER.  Move the cursor back to the left
to approximately the minimum and press ENTER.  The value 10 will be displayed for the number to minimize
cost.
6. Complementary or Substitute Product Determination:
Suppose that the demands of two products x sells for \$2.50 and product y sells for \$3.00 with unit prices p and q
are given by the following  equations:
x=8,000 - 0.09p² + 0.08p²
y=15000 + 0.04p² - 0.3q²
Are the products substitute complementary or neither.
The decision-making conditions are summarized in the following table:

 Partial Derivatives Products x and y ∂f/∂q  > 0 and  ∂f/∂p > 0 Substitute ∂f/∂q < 0 and ∂f/∂p < 0 Complementary ∂f/∂q > 0 and ∂f/∂p < 0 Neither ∂f/∂q < 0 and ∂f/∂p > 0 Neither

a) Press Y= and enter the following equations:
8000 - 0.09*2.50² +0.08x² opposite Y1 and
15000+ 0.04*x² -0.3*3².
b)  Move the cursor to the equal sign opposite Y2 and press ENTER to disable that equation; then press 0 for
ZoomFit to GRAPH the equation.
c)  Press 2nd, CALC, 6.
d)  ENTER 3 and press ENTER to get 0.48.
b)  Move the cursor to the equal sign opposite Y1and press ENTER to disable that equation; then move the cursor to Y2
and press ENTER to enable that equation.  Press ZoomFit to graph Y2.
e)  Press 2nd, CALC, 6.
d)  ENTER 2.5 and press ENTER to get 0.2
.
f)  Since we know that with substitute goods, all other things remaining constant, if the price of increases the demand for the other
increases.  In mathematical terms  we can express that as
∂f/∂q  > 0 and  ∂f/∂p > 0.  So, products x and y are substitute.

7.  Equality of Marginal Product of Labor and Capital.
The productivity of a manufacturing organization is given by f(x,y) = 15x0.4 y0.6 .  If the company is utilizing 400 units of
labor, what units of capital will make the marginal productivity of labor and the marginal productivity of capital equal? What is
the marginal rate at that level?
Take the partial derivatieves:  ∂f/∂x=6x-0.6 y0.6 and ∂f/∂y=9x0.4 y--0.4
a)  Press Y= and enter 6*400x^-0.6)x ^0.04 opposite Y1.  Opposite Y2, enter 9(400x^0.4)x ^-0.4.
b)  Press WINDOW and set Xmin =0, Xmax =700, Ymin =0 and Ymax=10.  Press ENTER to display the graph.
c)  Press 2ND, CALC, 5 (Intersect).
d)  When the graph appears, press ENTER, ENTER; move the cursor near the intersection and press ENTER again.
X=600 and Y=7.652..,  So, 600 units of capital and 400 units of labor will give marginal rates of 7.652.

8. Consumers' Surplus:
Assume the price-demand equation as follows of p=20-0.05x.  Find the consumers' surplus at \$8.
Note that we could integrate the function CS=(20-0.05x-8)dx, but I have chosen to simulate an actual integration and evaluate it
at both limits.  First, we need to find the upper limit of integration, that is, where the line y=8 intersects the demand curve.
a) Press Y= and enter the expression 20-0.05x opposite Y1.  Enter 8 opposite Y2.
b) Press WINDOW and set Xmin = 0, Xmax = 250, Ymin=6, Ymax=20.  Press GRAPH to graph the equations.
c) Press 2nd, CALC, 5 for Intersect.
d) On the graph that appears, press ENTER, ENTER; then move the cursor approximately to the intersection and press ENTER.
The intersection, 240 will be the upper limit of integration.
Now we want to integrate the areas separately.
a) Press Y= and move the cursor to the equal sign opposite Y2 and press ENTER to disable that equation. Press GRAPH.
b) Press 2nd, CALC, 7 for integration.  On the graph screen enter 0 for the lower limit and press ENTER.  Then ENTER 240 for
the upper limit and press ENTER. The value of the area, 3360, will be displayed.
c)  Press Y=, move the cursor to the equal sign opposite Y1 and press ENTER to disable that equation. Press GRAPH.
d) Press 2nd, CALC, 7 for integration.  On the graph screen enter 0 for the lower limit and press ENTER.  Then ENTER 240 for
the upper limit and press ENTER. The value of the area, 1920, will be displayed.
e)  The consumers' surplus, CS=3360-1920 =1440

9.  Producers' Surplus:

Assume the price-supply equation as follows of p=2+0.0002x².  Find the producers' surplus at \$20.
Note that we could integrate the function CS=(20-2 -0.0002x²)dx, but I have chosen to simulate an actual integration and evaluate it
at both limits.  First, we need to find the upper limit of integration, that is, where the line y=20 intersects the supply curve.
a) Press Y= and enter the expression 2+0.0002x² opposite Y1.  Enter 20 opposite Y2.
b) Press WINDOW and set Xmin = 0, Xmax = 300, Ymin=0, Ymax=25.  Press GRAPH to graph the equations.
c) Press 2nd, CALC, 5 for Intersect.
d) On the graph that appears, press ENTER, ENTER; then move the cursor approximately to the intersection and press ENTER.
The intersection, 268.33, will be the upper limit of integration.
Now we want to integrate the areas separately.
a) Press Y= and move the cursor to the equal sign opposite Y1 and press ENTER to disable that equation. Press GRAPH.
b) Press 2nd, CALC, 7 for integration.  On the graph screen enter 0 for the lower limit and press ENTER.  Then ENTER 268.33 for
the upper limit and press ENTER. The value of the area, 2146.66, will be displayed.
c)  Press Y=, move the cursor to the equal sign opposite Y1 and press ENTER to disable that equation. Press GRAPH.
d) Press 2nd, CALC, 7 for integration.  On the graph screen enter 0 for the lower limit and press ENTER.  Then ENTER 268.33 for
the upper limit and press ENTER. The value of the area, 5366.6, will be displayed.
e)  The suppliers' surplus, CS=5366.6-2146.66 =3219.94.

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