Answers to the Problems and Applications
1. William Gregg owned a mill in South Carolina. In December 1862, he placed a notice in the Edgehill Advertiser announcing his willingness to exchange cloth for food and other items. Here is an extract: 1 yard of cloth for 1 pound of bacon 2 yards of cloth for 1 pound of butter 4 yards of cloth for 1 pound of wool 8 yards of cloth for 1 bushel of salt
a. What is the relative price of butter in terms of wool?
1 pound of butter exchanged for 2 yards of cloth and 4 yards of cloth exchanged for 1 pound of wool. Hence 1 pound of butter exchanged for 2 yards of cloth and 2 yards of cloth exchanged for 1/2 pound of wool. So the relative price of butter in terms of wool was 1/2 pound of wool per pound of butter.
b. If the money price of bacon was 20¢ a pound, what do you predict was the money price of butter?
1 pound of bacon exchanged for 1 yard of cloth and 2 yards of cloth exchanged for 1 pound of butter. Hence it took 2 pounds of bacon to exchange for 1 pound of butter. As a result, if the money price of a pound of bacon was 20¢ the money price of 1 pound of butter was 40¢.
c. If the money price of bacon was 20¢ a pound and the money price of salt was $2.00 a bushel, do you think anyone would accept Mr. Gregg’s offer of cloth for salt?
If the money price of bacon is 20¢ a pound, Mr. Gregg’s offer to exchange 1 pound of bacon for 1 yard of cloth means that anyone could obtain 1 yard of cloth for a money price of 20¢. Mr. Gregg’s further offer to exchange 8 yards of cloth for 1 bushel of salt means that anyone could acquire 1 bushel of salt for $1.60, the price of 8 yards of cloth. If the money price of salt is $2.00 a bushel, many people would accept Mr. Gregg’s offer of cloth for salt because it enables them to obtain salt at a money price of only $1.60 a bushel.
2. The price of food increased during the past year.
a. Explain why the law of demand applies to food just as it does to all other goods and services.
The law of demand applies to food because there is both a substitution and an income effect that reinforce each other. When the price rises, people substitute to different foods. For instance, some might substitute home cooked meals for dining at a restaurant. And when the price rises, there is a negative income effect, so people they buy less of food overall and less food with the rising price. On both counts, the higher price of food decreases the quantity of food demanded.
b. Explain how the substitution effect influences food purchases and provide some examples of substitutions that people might make when the price of food rises and other things remain the same.
People substitute in two ways: They substitute cheaper foods for more expensive foods and also substitute diets for food.
c. Explain how the income effect influences food purchases and provide some examples of the income effect that might occur when the price of food rises and other things remain the same.
Food is a normal good so a rise in the price, which decreases people’s real incomes, decreases the quantity of food demanded. In the United States, restaurants suffer as the negative income effect from a higher price of food leads people to cut back their trips to restaurants. In poor countries, people literally eat less when the price of food rises and in extremely poor countries starvation increases.
3. Place the following goods and services into pairs of likely substitutes and into pairs of likely complements. (You may use an item in more than one pair.) The goods and services are: coal, oil, natural gas, wheat, corn, rye, pasta, pizza, sausage, skateboard, roller blades, video game, laptop, iPod, cell phone, text message, email, phone call, voice mail
Substitutes include: coal and oil; coal and natural gas; oil and natural gas; wheat and corn; wheat and rye; corn and rye; pasta and pizza; pasta and sausage; pizza and sausage (they type of sausage that cannot be used as a topping on pizza); skateboard and roller blades; skateboard and video game; roller blades and video game; text message and email; text message and phone call; and, email and phone call.
Complements include: pizza and sausage (the type of sausage that can be used as a topping on pizza); skateboard and iPod; roller blades and iPod; video game (the type played on a computer) and laptop; cell phone and text message; cell phone and phone call; cell phone and voice mail; and, phone call and voice mail.
4. During 2008, the average income in China increased by 10 percent. Compared to 2007, how do you expect the following would change:
a. The demand for beef? Explain your answer.
Beef is a normal good. The increase in income increases the demand for beef.
b. The demand for rice? Explain your answer.
Rice is probably an inferior good. The increase in income decreases the demand for rice.
5. In January 2007, the price of gasoline was $2.38 a gallon. By May 2008, the price had increased to $3.84 a gallon. Assume that there were no changes in average income, population, or any other influence on buying plans. How would you expect the rise in the price of gasoline to affect
a. The demand for gasoline? Explain your answer.
The rise in the price of gasoline does not change the demand for gasoline. The demand for gasoline changes only when some other relevant factor other than the price of the good changes.
b. The quantity of gasoline demanded? Explain your answer.
The rise in the price of gasoline decreases the quantity of gasoline demanded. A rise in the price of a good or service decreases the quantity of that good or service demanded.
6. In 2008, the price of corn increased by 35 percent and some cotton farmers in Texas stopped growing cotton and started to grow corn.
a. Does this fact illustrate the law of demand or the law of supply? Explain your answer.
This fact illustrates the law of supply: the higher price of corn lead some farmers to increase the quantity of corn they grow.
b. Why would a cotton farmer grow corn?
A cotton farmer would switch to corn because the profit from growing corn exceeds that from growing cotton. Cotton and corn are substitutes in production. A farmer making his or her decisions based on his or her self interest will respond to a rise in the price of corn by producing corn rather than cotton.
7. American to cut flights, charge for luggage American Airlines announced yesterday that it will begin charging passengers $15 for their first piece of checked luggage, in addition to raising other fees and cutting domestic flights as it grapples with record-high fuel prices.
Boston Herald, May 22, 2008
a. How does this news clip illustrate a change in supply? Explain your answer.
Fuel prices are a cost of a factor of production. As the cost rises, the supply decreases. American Airlines is decreasing the supply of its flights by cutting domestic flights.
b. What is the influence on supply identified in the news clip? Explain your answer.
The influence is the cost of a factor of production, in particular, the cost of fuel.
c. Explain how supply changes.
The increase in the cost of the factor of production decreases the supply and shifts the supply curve leftward.
8. Oil soars to new record over $135 The price of oil hit a record high above $135 a barrel on Thursday—more than twice what it cost a year ago ... OPEC has so far blamed price rises on speculators and says there is no shortage of oil.
BBC News 22 May 2008
a. Explain how the price of oil can rise even though there is no shortage of oil.
There is a shortage of oil if the price of oil is less than the equilibrium price. The equilibrium price of oil rises if the demand for oil increases and/or the supply decreases. So in these cases if the price of oil equals the equilibrium price, the price of oil rises and there is no shortage.
b. If a shortage of oil does occur, what does that imply about price adjustments and the role of price as a regulator in the market for oil?
If a persisting shortage of oil occurs, the implication is that price adjustments are slow so that the price is not an efficient regulator in the market for oil.
c. If OPEC is correct, what factors might have changed demand and/or supply and shifted the demand curve and/or the supply curve to cause the price to rise?
If OPEC is correct, speculators affect the current price of oil because they expect the price will be higher in the future. In this case the current demand for oil increases (as speculators buy oil to store for the future when the price is expected to be higher) and the current supply decreases (as speculators who already own oil store it to wait for the higher price expected in the future). The increase in current demand combined with the decrease in current supply raises the current price of oil.
9. “As more people buy computers, the demand for Internet service increases and the price of Internet service decreases. The fall in the price of Internet service decreases the supply of Internet service.” Is this statement true or false? Explain.
The statement is false for several reasons. First, if the demand for Internet services increases and nothing else changes, the price of Internet service will rise not fall. Second, if the price of Internet services falls, the supply of Internet services does not change. Rather, there is a decrease in the quantity supplied, that is, a movement along the supply curve rather than a shift of the supply curve.
10. The following events occur one at a time: (i) The price of crude oil rises. (ii) The price of a car rises. (iii) All speed limits on highways are abolished. (iv) Robots cut car production costs. Which of these events will increase or decrease (state which occurs)
a. The demand for gasoline?
(ii) and (iii) and (iv) change the demand for gasoline.
The demand for gasoline will change if the price of a car rises, all speed limits on highways are abolished, or robot production cuts the cost of producing a car. If the price of a car rises, the quantity of cars bought decrease and the demand for gasoline decreases. If all speed limits on highways are abolished, people will drive faster and use more gasoline. The demand for gasoline increases. If robot production plants lower the cost of producing a car, the supply of cars will increase. With no change in the demand for cars, the price of a car will fall and more cars will be bought. The demand for gasoline increases.
b. The supply of gasoline?
(i) changes the supply of gasoline.
The supply of gasoline will change if the price of crude oil (a factor of production used in the production of gasoline) changes. If the price of crude oil rises, the cost of producing gasoline rises and the supply of gasoline decreases.
c. The quantity of gasoline demanded?
(i) changes the quantity of gasoline demanded.
If the price of crude oil rises, the cost of producing gasoline rises and the supply of gasoline decreases. The demand for gasoline does not change. The price of gasoline rises and there is a movement up the demand curve for gasoline. The quantity of gasoline demanded decreases.
d. The quantity of gasoline supplied?
(ii) and (iii) and (iv) change the quantity of gasoline supplied.
If the price of a car rises, the quantity of cars bought decrease so the demand for gasoline decreases. The supply of gasoline does not change. The price of gasoline falls and there is a movement down the supply curve of gasoline. The quantity of gasoline supplied decreases.
If all speed limits on highways are abolished, people will drive faster and use more gasoline. The demand for gasoline increases. The supply of gasoline does not change, so the price of gasoline rises and there is a movement up along the supply curve. The quantity of gasoline supplied increases.
If robot production plants lower the cost of producing a car, the supply of cars will increase. With no change in the demand for cars, the price of a car will fall and more cars will be bought. The demand for gasoline increases. The supply of gasoline does not change, so the price of gasoline rises and the quantity of gasoline supplied increases. Price | Quantity demanded | Quantity supplied | (cents per pack) | (millions of packs a week) | 20 | 180 | 60 | 40 | 140 | 100 | 60 | 100 | 140 | 80 | 60 | 180 | 100 | 20 | 220 |
11. The demand and supply schedules for gum are given in the table.
a. Draw a graph of the gum market, label the axes and the curves, and mark in the equilibrium price and quantity.
Figure 3.1, on the next page, shows the demand and supply curves. The equilibrium price is 50 cents a pack, and the equilibrium quantity is 120 million packs a week. The price of a pack adjusts until the quantity demanded equals the quantity supplied. At 50 cents a pack, the quantity demanded is 120 million packs a week and the quantity supplied is 120 million packs a week.
b. Suppose that the price of gum is 70¢ a pack. Describe the situation in the gum market and explain how the price adjusts.
At 70 cents a pack, there is a surplus of gum and the price falls. At 70 cents a pack, the quantity demanded is 80 million packs a week and the quantity supplied is 160 million packs a week. There is a surplus of 80 million packs a week. The price falls until market equilibrium is restored at a price of 50 cents a pack.

c. Suppose that the price of gum is 30¢ a pack. Describe the situation in the gum market and explain how the price adjusts.
At 30 cents a pack, there is a shortage of gum and the price rises. At 30 cents a pack, the quantity demanded is 160 million packs a week and the quantity supplied is 80 million packs a week. There is a shortage of 80 million packs a week. The price rises until market equilibrium is restored at a price of 50 cents a pack.
d. A fire destroys some factories that produce gum and the quantity of gum supplied decreases by 40 million packs a week at each price. Explain what happens in the market for gum and illustrate the changes on your graph.
As the number of gum-producing factories decreases, the supply of gum decreases. There is a new supply schedule and, in Figure 3.2, the supply curves shifts leftward by 40 million packs at each price to the new supply curve S1. After the fire, the quantity supplied at 50 cents is now only 80 million packs, and there is a shortage of gum. The price rises to 60 cents a pack, at which the new quantity supplied equals the quantity demanded (100 million packs a week). So the new equilibrium price is 60 cents and the new equilibrium quantity is 100 million packs a week.
e. If at the time the fire occurs in d, there is an increase in the teenage population, which increases the quantity of gum demanded by 40 million packs a week at each price. What are the new equilibrium price and quantity of gum? Illustrate these changes in your graph.
The new price is 70 cents a pack, and the quantity is 120 million packs a week. The demand for gum increases and the demand curve shifts rightward by 40 million packs at each price. Supply decreases by 40 millions packs a week and the supply curve shifts leftward by 40 million packs at each price. These changes are shown in Figure 3.3 by the shift of the demand curve from D to D1 and the shift of the supply curve from S to S1. At any price below 70 cents a pack there is a shortage of gum. The price of gum rises until the shortage is eliminated.
12. Eurostar boosted by Da Vinci Code Eurostar, the train service linking London to Paris. . . , said on Wednesday first-half sales rose 6 per cent, boosted by devotees of the blockbuster Da Vinci movie.
CNN, July 26, 2006
a. Explain how Da Vinci Code fans helped to raise Eurostar’s sales.
The Da Vinci Code was placed in France and the United Kingdom and the movie was filmed in France and in the United Kingdom. Many fans celebrated the movie and book by holidaying in France and the United Kingdom in order to trace the path of the protagonists. These tourists increased the demand for train travel between London and Paris.
b. CNN commented on the “fierce competition from budget airlines.” Explain the effect of this competition on Eurostar’s sales.
Travel by budget airlines is a substitute for travel by Eurostar. Fierce competition from budget airlines means that the budget airlines have lowered the price of their fares. This fall in the price of a substitute decreases the demand for travel by Eurostar. Taken by itself, this factor decreased Eurostar’s sales.
c. What markets in Paris do you think these fans influenced? Explain the influence on three markets.
The Da Vinci Code movie fans were tourists in Paris and so increased the demand for tourist activities. The increase in tourists in Paris increased the demand for restaurant meals, increased the demand for lodging, and increased the demand for transportation within Paris.
13. Of gambling, grannies and good sense Nevada has the fastest growing elderly population of any state. . . . Las Vegas has . . . plenty of jobs for the over 50s.
The Economist, July 26, 2006 Explain how grannies have influenced the
a. Demand side of some Las Vegas markets.
On the average, elderly people require more health care services than younger people. So the influx of older people into Las Vegas increased the demand for medical services and pharmaceutical drugs and services. Older people also eat out more often and do less yard work. So the demand for restaurant meals and yard care maintenance increased.
b. Supply side of other Las Vegas markets.
Older but not-yet retired people work, so the increase in “grannies” increased the supply of labor.