Question

A man walks to his office at 5 km/hr and then goes back on a rickshaw at 15 km/hr. Find the average speed for the whole journey

Answer 1

The average speed is $v = 2 d / t$, where $d$ is the distance to the office, and $t$ is the time of travel to the office and back. The walking speed is $v_0 = 5 \, \text{km} / \text{hr}$, and the rickshaw speed is $15\, \text{km} / \text{hr} = 3 v_0$. Hence, the total travel time is $t = d/v_0 + d / 3 v_0 = 4 d / 3 v_0$. From this, we find the average speed: $v = 2 d / t = 3 v_0 / 2 = 7.5\, \text{km} / \text{hr}$.

Answer: 7.5 km/hr