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Department of Economics
Boğaziçi University
EC 205 Macroeconomics I
Fall 2015
Problem Session 1 Solutions
Q1 Abby consumes only apples. In year 1, red apples cost $1 each, green apples cost
$2 each, and Abby buys 10 red apples. In year 2, red apples cost $2, green apples cost
$1, and Abby buys 10 green apples.
a. Compute a consumer price index for apples for each year. Assume that year 1 is the
base year in which the consumer basket is fixed. How does your index change from
year 1 to year 2?
b. Compute Abby’s nominal spending on apples in each year. How does it change from
year 1 to year 2?
c. Using year 1 as the base year, compute Abby’s real spending on apples in each year.
How does it change from year 1 to year 2?
d. Defining the implicit price deflator as nominal spending divided by real spending,
compute the deflator for each year. How does the deflator change from year 1 to year
2?
A1
Thus, the implicit price deflator suggests that prices have fallen by half. The
reason for this is that the deflator estimates how much Abby values her apples
using prices prevailing in year 1. From this perspective green apples appear very
valuable. In year 2, when Abby consumes 10 green apples, it appears that her
consumption has increased because the deflator values green apples more
highly than red apples. The only way she could still be spending $10 on a higher
consumption bundle is if the price of the good she was consuming fell.
Q2 Consider an economy that produces and consumes bread and automobiles. In the
following table are data for two different years.
a. Using the year 2000 as the base year, compute the following statistics for each year:
nominal GDP, real GDP, the implicit price deflator for GDP, and a fixed-weight price
index such as the CPI.
b. How much have prices risen between 2000 and 2010? Compare the answers given
by the Laspeyres and Paasche price indexes. Explain the difference.
c. Suppose you are a senator writing a bill to index Social Security and federal pensions.
That is, your bill will adjust these benefits to offset changes in the cost of living. Will
you use the GDP deflator or the CPI? Why?
b. The implicit price deflator is a Paasche index because it is computed with a changing
basket of goods; the CPI is a Laspeyres index because it is computed with a fixed basket
of goods. From (6.a.iii), the implicit price deflator for the year 2010 is 1.52, which
indicates that prices rose by 52 percent from what they were in the year 2000. From
(6.a.iv.), the CPI for the year 2010 is 1.6, which indicates that prices rose by 60 percent
from what they were in the year 2000. If prices of all goods rose by, say, 50 percent,
then one could say unambiguously that the price level rose by 50 percent. Yet, in our
example, relative prices have changed. The price of cars rose by 20 percent; the price
of bread rose by 100 percent, making bread relatively more expensive. As the
discrepancy between the CPI and the implicit price deflator illustrates, the change in
the price level depends on how the goods’ prices are weighted. The CPI weights the
price of goods by the quantities purchased in the year 2000. The implicit price deflator
weights the price of goods by the quantities purchased in the year 2010. The quantity
of bread consumed was higher in 2000 than in 2010, so the CPI places a higher weight
on bread. Since the price of bread increased relatively more than the price of cars, the
CPI shows a larger increase in the price level.
c. There is no clear-cut answer to this question. Ideally, one wants a measure of the
price level that accurately captures the cost of living. As a good becomes relatively
more expensive, people buy less of it and more of other goods. In this example,
consumers bought less bread and more cars. An index with fixed weights, such as the
CPI, overestimates the change in the cost of living because it does not take into account
that people can substitute less expensive goods for the ones that become more
expensive. On the other hand, an index with changing weights, such as the GDP
deflator, underestimates the change in the cost of living because it does not take into
account that these induced substitutions make people less well off.
Q3. What is a market-clearing model? When is it appropriate to assume that markets
clear?
A market-clearing model is one in which prices adjust to equilibrate supply and
demand. Market-clearing models are useful in situations where prices are flexible. Yet
in many situations, flexible prices may not be a realistic assumption. For example, labor
contracts often set wages for up to three years. Or, firms such as magazine publishers
change their prices only every three to four years. Most macroeconomists believe that
price flexibility is a reasonable assumption for studying long-run issues. Over the long
run, prices respond to changes in demand or supply, even though in the short run they
may be slow to adjust.
Q4. Use the model of supply and demand to explain how a fall in the price of frozen
yogurt would affect the price of ice cream and the quantity of ice cream sold. In your
explanation, identify the exogenous and endogenous variables.
We can use a simple variant of the supply-and-demand model for pizza to answer this
question. Assume that the quantity of ice cream demanded depends not only on the
price of ice cream and income, but also on the price of frozen yogurt:
Qd = D(PIC, PFY, Y).
We expect that demand for ice cream rises when the price of frozen yogurt rises,
because ice cream and frozen yogurt are substitutes. That is, when the price of frozen
yogurt goes up, I consume less of it and, instead, fulfill more of my frozen dessert urges
through the consumption of ice cream. The next part of the model is the supply
function for ice cream, Qs = S(PIC). Finally, in equilibrium, supply must equal demand,
so that Qs = Qd. Y and PFY are the exogenous variables, and Q and PIC are the
endogenous variables. Figure 1–1 uses this model to show that a fall in the price of
frozen yogurt results in an inward shift of the demand curve for ice cream. The new
equilibrium has a lower price and quantity of ice cream.
Exogenous variables are the ones that are determined outside our model, such as the
price of frozen yogurt here
But the quantity and the price of the ice cream are endogenous variables, since they
are determined in our model