Essentials of Economics 7th Edition by Gregory Mankiw

Exercise 10

Which of the following might lead to an increase in the equilibrium price of jelly and a decrease in the equilibrium quantity of jelly sold?
A) an increase in the price of peanut better, a complement to jelly
B) an increase in the price of Marshmallow Fluff, a substitute for jelly
C) an increase in the price of grapes, an input into jelly
D) an increase in consumers' incomes, as long as jelly is a normal good