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A person covers 25% of the distance at the speed of 5 km/hr and 1/3rd of the remaining distance covers at the speed of 25 km/hr and remaining distance covers at the speed of 10 km/hr. What is the average speed of the person in whole journey?
1. 100/9 km/hr
2. 100/11 km/hr
3. 100/7 km/hr
4. 100/13 km/hr

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Best answer
Correct Answer - Option 2 : 100/11 km/hr

Given:

A person covers 25% of the distance at the speed of 5 km/hr

He covers 1/3rd of the remaining at the speed of 25 km/hr

He covers remaining distance at the speed of 10 km/hr

Formula:

Average speed = Total distance/Total time

Calculation:

Let total distance be 100 km

25% of the distance = 100 × (25/100) = 25 km

Remaining distance = 100 - 25 = 75 km

1/3rd of the 75 = 25 km

Remaining distance = 100 - 25 - 25 = 50 km

Time taken by person to cover 25 km distance at the speed of 5 km/hr = 25/5 = 5 hrs

Time taken by person to cover 25 km distance at the speed of 25 km/hr = 25/25 = 1 hr

Time taken by person to cover 50 km distance at the speed of 10 km/hr = 50/10 = 5 hrs

Total time = 5 + 1 + 5 = 11 hrs

∴ Average speed = 100/11 km/hr

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