While travelling from A to B, Raghav travels a quarter of the distance at 10 km/h, the next quarter of the distance at 15 km/h, the third quarter of the distance at 20 km/h, and the final quarter of the distance at 30 km/h. While travelling on exactly the same route, Manish travels for a quarter of the total time taken for his journey at 10 km/h, the next quarter of the total time taken for his journey at 15 km/h, the third quarter of the total time taken for his journey at 20 km/h, and the final quarter of the total time taken for his journey at 30 km/h. If the overall average speed of Raghav during his journey is given as y km/h, and that of Manish is given as z km/h, find the value of (z – y).
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 2.75.
Let each quarter distance = D km and total distance = 4D km
Total time taken by Raghav = D/10 + D/15 + D/20 + D/30 = D/4 hours
Raghav's average speed (y) = 4D/(D/4) = 16 km/h
Let the total time taken by Manish = 4T and each quarter time = T
Total distance covered by Manish = 10T + 15T + 20T + 30T = 75T km
Manish's average speed (z) = (75T)/(4T) = 18.75 km/h
So, (z - y) = 18.75 - 16 = 2.75