ECOS2001 – Intermediate Microeconomics Tutorial 2
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ECOS2001-Intermediate Microeconomics
Tutorial 2- Answer Key
Chapter 4
Question 1
Joe's utility function for movies at the theater (T) and DVDs watched at home (D) is given by
U=4T²+D²(MU,=8Tand MUp=2D)
1. Write an equation for MRSrD.
2. Would bundles of (T=2 and D=2)and(T=1 and D=4) be on the same indifference curve?
3. Are Joe's indifference curves convex?(Does MRSrp fall as Trises?)
Solution:
1. Using the equation for MRSro, we find
2. For bundles to lie on the same indifference curve, they must provide the same level of utility.
For the first bundle: U(T=2,D=2)=4(2)²+(2)²=4(4)+4=16+4=20.
For the second bundle:U(T=1,D=4)=4(1)²+(4)²=4(1)+16=4+16=20.
Because the bundles provide the same level of utility, they must lie on the same indifference curve.
3. To answer this question, calculate MRSro at each of the bundles; remember
MRSrD=4T/D.
When T=1 and D=4:MRSrD=4T/D=4(1)/4=1
When T=2 and D=2:MRSrD=4T/D=4(2)/2=4
So, Joe is willing to trade more DVD-watching for fewer theater tickets as he watches more movies in the theater. What does this mean? Joe's indifference curves are actually concave, not convex, violating the fourth characteristic of indifference curves.
Question 2
James has $40 per week he can spend on movie tickets (M)at $10 each or burritos (B) at $5 each.
a. Write an equation for James's budget constraint and draw it on a graph that has burritos on the horizontal axis.
b. Suppose the price of burritos rises to $8.Draw James's new budget constraint.
Solution
a. The budget constraint represents bundles James can feasibly purchase, and takes the form:
Income =PBB+PMM
40=5B+10M
Since we are putting burritos on the horizontal axis, we want to find an equation for M as a function of B, or
10M=40-5B
M=4-0.5B
b. To find the new budget constraint, simply change the price of burritos to $8.
Since the price of movie tickets has not changed, we know the budget constraint will pivot inward, to a new horizontal intercept of 5 burritos.
Question 3
Sarah gets utility from soda (S) and hotdogs (H); her utility function is given by
U=S⁰ .5H⁰ .5
Sarah's income is $12, and the prices of sodas and hotdogs are $2 and $3, respectively. What is Sarah's utility-maximizing bundle of sodas and hotdogs?
Solution
The tangency condition for maximization is
Substituting in the parameters yields
So
To find the exact quantities, use the budget constraint:
Income=PsS+PmH or 12=2S+3H
S=3 and H =2
Question 4
Draw two indifference curves for each of the following pairs of goods. Put the quantity of the 1st good on the horizontal axis and the quantity of the 2nd good on the vertical axis.
a. Paul likes pencils and pens but does not care which he writes with. b. Rhonda likes carrots and dislikes broccoli.
c. Emily likes hip-hop iTunes downloads and doesn't care about heavy metal downloads.
d. Michael only likes dress shirts and cufflinks in 1 to 1 proportions.
e. Carlene likes pizza and shoes.
f. Steven dislikes both fish and potatoes.
Solution
In the figures that follow, bundles along the indifference curve labeled U2 are strictly preferred to bundles along the indifference curve Ui.
a. Paul is equally as happy with a pen as with a pencil. Therefore, these two goods are perfect substitutes.
Pencils
b. Carrots are a good and broccoli is a bad for Rhonda.
Broccoli
Carrots
c. Hip-hop is a good, heavy metal is a neutral.
Heavy
metal
music
Hip-hop music
d. Dress shirts and cufflinks are perfect complements.
e. Both pizza and shoes are good for Carlene.
Pizza
f. Steven's indifference curves are downward-sloping; if you give Steven 1 more fish,
it will reduce his utility, so to keep his utility constant, you must increase his utility by taking away some of the potatoes he dislikes.
Fish
Potatoes
Question 5
José gets satisfaction from both music and fireworks. Jose's income is $240 per week. Music costs $12 per CD, and fireworks cost $8 per bag.
a. Graph the budget constraint José faces, with music on the vertical axis and fireworks on the horizontal axis.
b. If José spends all his income on music, how much music can he afford? Plot a point that illustrates this scenario.
c. If Jose spends all his income on fireworks, how many bags of fireworks can he afford? Plot a point that illustrates this scenario.
d. If José spends half his income on fireworks and half his income on music, how much of each can he afford? Plot a point that illustrates this scenario.
e. Connect the dots to create Jose's budget constraint. What is the slope of the budget constraint?
f. Divide the price of fireworks by the price of music. Have you seen this number before and, if so, where?
g. Suppose that a holiday bonus temporarily raises Jose's income to $360. Draw Jose's new budget constraint.
h. Indicate the new bundles of music and fireworks that are feasible, given Jose's new income.
Solution
Jose has income of I=$240, the price of music is Px=$12,and the price of fireworks is P,=$8.
.
(Bags)
b.
This is shown as the point labeled b in the figure below.
C.
This is shown as the point labeled c in the figure below.
d.
This is shown as the point labeled d in the figure below.
.
(Bags)
The slope of the budget constraint is
f
.
This is - 1 times the slope of the budget constraint.
g.
(Bags)
h
.
(Bags)
The shaded area shows the new bundles of music and fireworks that are feasible for
Jose.
Question 6
Find the utility-maximizing bundle for a Cobb Douglas utility function U(X,Y)= x⁴Y¹-a where X and Y denote two goods and "a"is the preference parameter. Assume that Px and
Py denote the price of good X and Y, respectively, and I denotes the income.
Solution
There are two approaches to solving the consumer's utility-maximization problem using calculus. The first relies on what we already demonstrated in this chapter: At the optimum, the marginal rate of substitution equals the ratio of the two goods'
prices. First, take the partial derivatives of the utility function with respect to each of the goods to derive the marginal utilities:
Next, use the relationship between the marginal utilities and the marginal rate of substitution to solve for M RS xy and simplify the expression:
Find Yas a function of Xby setting MRSxy equal to the ratio of the prices:
,where is a constant
Now that we have the optimal relationship between Y and X, substitute the
expression for Y into the budget constraint to solve for the optimal consumption
bundle:
Question 7
Eric's utility function is u(x,y)= 3x+4y and faces prices px=$1 and py=$2.5 and income I=$23.Comparing his MRSxyand the price ratio, find his optimal consumption of goods x and y.(Corner solution!)
Solution
· First, we need to calculate Eric's marginal rate of substitution,
and compare it to the ratio of prices,
- Since Eric receives more benefit by solely consuming good x. Alterna- tively, the "bang for the buck"he obtains from good x, is larger than that for good y, ,inducing him to keep increasing his
purchases of good x, while reducing those of good y, until he only consumes the former.
- In this case, Eric can consume
Question 8
John's utility function is u(x,y)=5 min{2x;3y} and he faces prices px=$1 and py=$2 and income I=$100.Find his optimal consumption of goods x and y.
Solution
· Since we cannot define John's marginal rate of substitution, we must use the fact that John prefers to consume goods x and y in fixed proportions to maximize his utility (i.e., the two arguments inside the min operator must coincide, 2x =3y) or, after dividing both sides by 2,
This is the kink of John's indifference curves, as depicted in the following figure.
● Using the condition we found above, ,and John's budget line,x+2y =100, we can substitute for x, giving the equation
-Combining terms on the lef-hand side of the equation gives us Di-
viding both sides of this expression by provides our equilibrium consumption level of good y, y =28.57 units.
· Returning to our condition for John's consumption bundle, we can plug in our value of y =28.57 to find our equilibrium consumption level of good x,
2023-06-19