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A person standing on a railway platform noticed that a train took 21 seconds to completely pass through the platform which was 84 m long and it took 9 seconds in passing him. The speed of the train was
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- 25.2 km/hour
- 32.4 km/hour
- 50.4 km/hour
- 75.6 km/hour
Correct Option: A
Let the length of train be x metres.
When the train crosses the standing man,
| its speed = | |
| 9 |
When the train crosses the platform of length 84 m, its speed
| = | |
| 21 |
| Obviously, | = | ||
| 9 | 21 |
⇒ 21x – 9x = 9 × 84
⇒ 12x = 9 × 84
| ⇒ x = | = 63 m | |
| 12 |
| ∴ Required speed = | m/sec | |
| 9 |
| = | × | kmph = 25.2 kmph | ||
| 9 | 5 |
