One third of a certain journey is covered at the rate of 25 km/hr, one forth at the rate of 30 km/hr and the rest at 50 km/hr. The average speed for the whole journey is :

Answer: Option B

Solution

Answer: Option B

Solution:

Let the total distance = 1200 km


$$\begin{array}{rl}& \text{Total time taken :}\\ & =\frac{400}{25}+\frac{300}{30}+\frac{500}{50}\\ & =16+10+10\\ & =\text{ 36 hours}\\ & \therefore \text{Average speed}\\ & =\frac{\text{Total distance }}{\text{Total time}}\\ & =\frac{1200}{36}\\ & =33\frac{1}{3}\text{ km/hr}\end{array}$$