Bunuel wrote:

A car has been driven with an average speed of 30 kilometers per hour during the first 30 kilometers of a journey. Upon reaching the 30th kilometer, the car then travels at 45 kilometers per hour for the next 30 kilometers. Find out the average speed of the car if it has not been stopped at all during the journey.

(A) 35

(B) 36

(C) 37.5

(D) 38

(E) 40

Average speed = \(\frac{TotalDistance}{TotalTime}\)

Total distance is 60 km

We need time for each segment.

RT = D, so T = D/R

For both segments: Time = \(\frac{Distance}{Rate}\)

Time, Segment 1: \(\frac{30km}{30kmh} = 1 hour\)

Time, Segment 2: \(\frac{30km}{45kmh}=\frac{2}{3}hour\)

Total time: \((1 + \frac{2}{3})=\frac{5}{3}hours\)

Average speed=

\(\frac{TotalD}{TotalT}=\frac{60}{(\frac{5}{3})}=(60 * \frac{3}{5})=36\)

Answer B