Problem Solving

sanju09 wrote:A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon of gasoline when driven on the highway. According to these rates, which of the following is closest to the number of miles per gallon that the car averages when it is driven 10 miles in the city and then 50 miles on the highway?
(A) 28
(B) 30
(C) 33
(D) 36
(E) 38

Gasoline required for 10 mile drive in the city in gallons = (Miles driven)/(Miles per gallon) = 10/25 = 2/5
Gasoline required for 50 mile drive on the highway in gallons = (Miles driven)/(Miles per gallon) = 50/40 = 5/4

Total miles driven = (50 +10) = 60
Total gallons of Gasoline required = (2/5 + 5/4) = 33/20

Miles per gallon that the car averages = 60/(33/20) = (20*60)/33 = 400/11 ≈ 36

The correct answer is D.