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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 hours2. 15 hours3. 20 hours4. 40 hours5. 25 hours |
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Answer» Correct Answer - Option 3 : 20 hours Given: Speed in 1st half is 15 km/h Speed in 2nd 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 1st part of journey y = speed during 2nd 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 |
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