Suppose the price of gasoline in July 2004 averaged $1.35 a gallon and 15 million gallons a day were sold. In October 2004, the price averaged $2.15 a gallon and 14 million gallons were sold. If the demand for gasoline did not shift between these two months, use the midpoint formula to calculate the price elasticity of demand. Indicate whether demand was elastic or inelastic.

0.15

Inelastic

Explanation:

Price elasticity of demand measures the responsiveness of quantity demanded to changes in price of the good.

Price elasticity of demand = midpoint change in quantity demanded / midpoint change in price  

Midpoint change in quantity demanded = change in quantity demanded / average of both demands

change in quantity demanded = 14 million  - 15 million =  -1 million  

average of both demands = (14 million + 15 million  ) / 2 = 14.50 million

Midpoint change in quantity demanded =  -1 million  / 14.50 million = -0.069

midpoint change in price = change in price / average of both price

change in price = $2.15 - $1.35 = $0.80

average of both prices = ( $2.15 + $1.35 ) / 2 = $1.75

midpoint change in price = $0.80 /  $1.75 = 0.457

-0.069 / 0.457 = 0.15 demand is inelastic  

If the absolute value of price elasticity is greater than one, it means demand is elastic. Elastic demand means that quantity demanded is sensitive to price changes.  

Demand is inelastic if a small change in price has little or no effect on quantity demanded. The absolute value of elasticity would be less than one

Demand is unit elastic if a small change in price has an equal and proportionate effect on quantity demanded.  

Infinitely elastic demand is perfectly elastic demand. Demand falls to zero when price increases  

Perfectly inelastic demand is demand where there is no change in the quantity demanded regardless of changes in price.