A motorist travels to a place 150 km away at an average speed of 50 km/hr and returns at 30 km/hr. His average speed for the whole journey in km/hr is :

A motorist travels to a place 150 km away at an average speed of 50 km/hr and returns at 30 km/hr. His average speed for the whole journey in km/hr is :

A 39

B 37.5

C 31

D 45

Solution

Correct Answer: Option B

Average speed = \(\frac{2xy}{x\;+\;y}\) km/hr

= \(\frac{2\times50\times30}{50+30}\) km/hr.

= 37.5 km/hr.