1.

A man covers 1 / 4th of the distance at the speed of 10 km / hr, next 1 / 4 covers at the speed of 20 km / hr, next 1 / 4 covers at the speed of 40 km / hr and remaining distance covers at the speed of 8 km / hr. What is the average speed of the man in whole journey?1. 40 / 7 km / hr2. 40 / 3 km / hr3. 53 / 5 km / hr4. 71 / 3 km / hr

Answer» Correct Answer - Option 2 : 40 / 3 km / hr

Given:

A man covers 1 / 4th of the distances at the speed of 10 km / hr, 20 km / hr, 40 km / hr and 8 km / hr

Formula:

Average speed = Total distance / Total time

Calculation:

Let total distance be 160 km.

1 / 4 of 160 = 40 km

Time take to covers 40 km distance at the speed of 10 km / hr = 40 / 10 = 4 hrs

Time take to covers 40 km distance at the speed of 20 km / hr = 40 / 20 = 2 hrs

Time take to covers 40 km distance at the speed of 40 km / hr = 40 / 40 = 1 hr

Time take to covers 40 km distance at the speed of 8 km / hr = 40 / 8 = 5 hrs

Total time = 4 + 2 + 1 + 5 = 12 hrs

∴ Average speed = 160 / 12 = 40 / 3 km / hrs


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