1. Which of the following combinations of goods are complements and which are substitutes?  Could they be either in different circumstances?  Discuss.

a. a mathematics class and an economics class

b. tennis balls and a tennis racket

c. steak and lobster

d. a plane trip and a train trip to the same destination

e. bacon and eggs

2. Suppose that a consumer spends a fixed amount of income per month on the following pairs of goods: 

a. tortilla chips and salsa;

b. tortilla chips and potato chips;

c. movie tickets and gourmet coffee;

d. travel by bus and travel by subway. 

If the price of one of the goods increases, explain the effect on the quantity demanded of each of the goods.  In each pair, which are likely to be complements and which are likely to be substitutes?