A man covers 1/4th of a distance with the speed of 25 km/hr and 50% of the distance covers with the speed of 10 km/hr and the rest of the distance covers with the speed of 12.5 km/hr. What is the average speed of the man in the whole journey?

Option 4 : 12.5 km/hr

Given:

Man covers 1/4^th of distance with the speed of = 25 km/hr

Man covers 50% of distance with the speed of = 10 km/hr

Rest distance covers with the speed of = 12.5 km/hr

Formula:

Average speed = Total distance/Total time

Calculation:

Let total distance be 100 km

1/4^th of 100 km = 100 × 1/4 = 25 km

50% of 100 km = 100 × 50/100 = 50 km

Remaining distance = 100 – 25 – 50 = 25 km

Time to cover 1/4^th of the distance with the speed of 25 km/hr

= 25/25 = 1 hr

Time to cover 50% of the distance with the speed of 10 km/hr

= 50/10 = 5 hrs

Time to cover remaining distance with the speed of 12.5 km/hr

= 25/12.5 = 2 hrs

Total distance = 100 km

Total time = 1 hr + 5 hr + 2 hr = 8 hrs

∴ Average speed = 100/8 = 12.5 km/hr