Question

Ram covers a distance of 150 kilometres. He covers the first half of the journey by bicycle at a speed of 15 km/h. He completes the remaining half by walking at a speed of 5 km/h. Calculate the time taken by Ram to cover the whole distance.

1. 10 hours
2. 15 hours
3. 20 hours
4. 40 hours
5. 25 hours

Answer 1

Correct Answer - Option 3 : 20 hours

Given:

Speed in 1^st half is 15 km/h

Speed in 2^nd half is 5 km/h

Total distance covered is 150 km

Formula:

Average speed for a journey when distances are equal is S = 2{xy/(x + y)}

Where,

S =average velocity

x = speed during 1^st part of journey

y = speed during 2^nd part of journey

Calculation:

Average speed for the whole journey = 2 × {(15 × 5)/(15 + 5)} km/h

⇒ Average speed = 2 × (75/20) km/h

⇒ Average speed = (75/10) km/h

Time to cover the distance = 150/(75/10) hours

⇒ Time = (150 × 10)/75 hours

⇒ Time = 20 hours

∴ Time taken to cover the distance is 20 hours