-
One third of a certain journey is covered at the rate of 25 km/hour, one-fourth at the rate of 30 km/hour and the rest at 50 km/hour. The average speed for the whole journey is
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- 35 km/hour
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33 1 km/hr 3 - 30 km/hour
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37 1 km/hr 12
Correct Option: B
Let the total distance be x km.
| Total time = | |||||
| + | + | ||||
| 25 | 30 | 50 |
| = | + | + | |||
| 75 | 120 | 120 |
| = | + | ||
| 75 | 60 |
| = | = | hours | ||
| 300 | 100 |
| ∴ Average speed = | |
| Time taken |
= | |||||
| 100 | |||||
| = | = 33 | kmph | ||
| 3 | 3 |
Second Method :
Here, x = 3, u = 25, y = 4, v = 30
| z = | , w = 50 | |
| 5 |
| Average Speed = | |||||
| + | + | ||||
| xu | yv | zw | |||
| = | |||||
| + | + | ||||
| 3 × 25 | 4 × 30 | (12/5) × 50 | |||
| = | |||||
| + | + | ||||
| 75 | 120 | 120 | |||
| = | |||||
| + | |||||
| 75 | 60 | ||||
= | |||||
| 300 | |||||
| = | = | ||
| 9 | 3 |
| = 33 | km/hr. | |
| 3 |
