Question

A bus is travelling the first 1/3 rd distance at a speed of 10 km/h. The next 1/4 at 20 km/h and the remaining at 40 km/h. Find the average speed of the bus?

Answer 1

If total distance is S then

Average speed = Total distance / Time
= S / (t1 + t2)
= S / [(S/(3 * 10)) + (S/(4 * 20)) + (5S/(12 * 40))]
...….....[∵ Time = Distance / Speed]
= 1 / (1/30 + 1/80 + 5/480)
= 17.7 kmph

In two significant figures average speed will be 18 kmph