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

Answer:

The correct option is B.

Step-by-step 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.

$Time=\frac{Distance}{Speed}$

Time taken by Susan in first 30 miles is

$T_1=\frac{30}{30}=1$

Time taken by Susan in remaining 30 miles is

$T_2=\frac{30}{60}=0.5$

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

$S=\frac{60}{1.5}=40$

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