Word Problem

Question

The fuel efficiency F for a particular car is given by F(x)= -0.018x² + 1.656x + 4.4 where x is the speed of the car in miles per hour (mph) and F(x) is the corresponding fuel efficiency in miles per gallon (mpg). What speed will yield the maximum fuel efficiency?

Answer 1

Since the function here is an upside down parabola, the maxilum occurs at the vertex; x_vertex = -b/(2a).  Use that x value in s(x) to obtain maximum mpg value.