The fuel economy of a car, measured in miles per gallon, is modeled by the function ƒ(s) = –0.009s2 + 0.699s + 12 where s represents the average speed of the car, measured in miles per hour. what average speed results in the maximum fuel economy? a. 25.57 miles per hour b. −38.83 miles per hour c. 38.83 miles per hour d. 3.88 miles per hour

ANSWER

C. 38.83 miles per hour.

EXPLANATION

It was given that, the fuel economy of a car, measured in miles per gallon, is modeled by the function



We rewrite the function in the vertex form by completing the square.







Or



The vertex of this function is



Hence the maximum fuel economy is 25.57 gallons and this occurred at an average speed of 38.83.

The correct answer is C