A certain car averages 25 miles per gallon when driving in the city

A certain car averages 25 miles per gallon when driving in the city and 40 miles to the gallon when driving 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 50 miles on the highway?
 
a)28
b)30
c)33
d)36
e)38
 

Using weighted averages:

Avg Miles/ Gallon = 10 + 15 / (10/25  +  40/50)  = 60/(33/20) ~ 36.

Ans : d