A man covers a certain distance by bike. If he covers 25% of the distance at the speed of 25 km/h, 50% of the distance at the speed of 50 km/h, and the remaining distance at the speed of 12.5 km/h, find his average speed over the whole journey.
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 25 km/h.
We know that,
Average speed = Total distance/Total time
Let the total distance be 100 km
He covers 25% of the distance at the speed of 25 km/h = 25% of 100 = 25 km
⇒ Time = 25/25 = 1 hr
50% of the distance at the speed of 50 km/h = 50% of 100 = 50 km
⇒ Time = 50/50 = 1 hr
The remaining distance at the speed of 12.5 km/h
Remaining distance = 100 - 25 - 50 = 25 km
⇒ Time = 25/12.5 = 2 hr
Average speed = 100/(1 + 1 + 2) = 100/4 = 25 km/hr