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Speed of motorboat in still water is 45kmph. If the motorboat travels 80 km along the stream in 1 hour 20 minutes, then the time taken by it to cover the same distance against the stream will be
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- 3 hours
- 1 hour 20 minutes
- 2 hours 40 minutes
- 2 hours 55 minutes
- 3 hours
Correct Option: C
Let the speed of the current be p kmph
Speed of motorboat in still water = 45kmph
∴ Rate downstream = (p + 45) kmph.
According to the question,
| = 1 hour 20 minutes = | hours | |||
| p + 45 | 3 |
⇒ 4p + 180 = 240
⇒ 4p = 240 – 180 = 60
| ⇒ p = | kmph = 15 kmph | |
| 4 |
Rate upstream = 45 – 15 = 30 kmph
| ∴ Required time = | hours | |
| 30 |
| Required time = | = 2 hour 40 minutes | |
| 3 |
