試題詳解

1. (5%) For speeds between 40 and 65 kilometers per hour, a truck gets 480/x kilometers for per liter of diesel gasoline when driven at a constant speed of x kilometers per hour. Diesel gasoline costs $2.23 per liter, and the driver is paid $15.10 per hour. What is the most economical constant speed between 40 and 65 kilometers per hour at which to drive the truck?
(A)52.5 kilometers per hour
(B) 57 kilometers per hour
(C) 65 kilometers per hour
(D) None of the above