Question

Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip if she made no stops during the trip what was susan's avg speed in miles/hr for the entire trip.(A) 35(B) 40(C) 45(D) 50(E) 55

Answer 1

The correct option is B.

Explanation:

It is given that Susan drove an average speed of 30 miles per hour for the first 30 miles of a trip & then at a average speed of 60 miles/hr for the remaining 30 miles of the trip.

`Time=(Distance)/(Speed)`

Time taken by Susan in first 30 miles is

`T_1=(30)/(30)=1`

Time taken by Susan in remaining 30 miles is

`T_2=(30)/(60)=0.5`

Total distance covered by Susan is

`D=30+30=60`

Total time taken by susan to complete 60 miles trip is

`T=T_1+T_2`

`T=1+0.5=1.5`

Susan's avg speed in miles/hr for the entire trip is

`S=(60)/(1.5)=40`

The average speed of susan for entire trip is 40. Therefore the correct option is B.