When the Price of a Glass of Lemonade at a Lemonade

Multiple Choice

When the price of a glass of lemonade at a lemonade stand was $1.75, 400 glasses were sold. When the price was lowered to $1.50, 500 glasses were sold. Assume that the demand function is linear and that the marginal and fixed costs are $0.10 and $ 25, respectively. Find the marginal profit when 300 glasses of lemonade are sold and when 700 glasses of lemonade are sold.

A) $P ^ { \prime } ( 300 ) = 1.15 , P ^ { \prime } ( 700 ) = - 0.85$
B) $P ^ { \prime } ( 300 ) = - 0.85 , P ^ { \prime } ( 700 ) = 1.15$
C) $P ^ { \prime } ( 300 ) = 1.15 , P ^ { \prime } ( 700 ) = 0.85$
D) $P ^ { \prime } ( 300 ) = 0.85 , P ^ { \prime } ( 700 ) = - 1.15$
E) $P ^ { \prime } ( 300 ) = - 1.15 , P ^ { \prime } ( 700 ) = - 0.85$