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A motor boat covers a certain distance downstream in a river in 3 hours. It covers the same distance upstream in 3 hours and a half. If the speed of water is 1.5 km/h, then the speed of the boat in still water is :
-
- 17 km/h
- 19.5 km/h
- 17.5 km/h
- 19 km/h
- 17 km/h
Correct Option: B
Let the speed of boat in still water be p kmph and the distance be q km.
∴ Rate downstream = (p + 1.5) kmph
Rate upstream = (p – 1.5) kmph
According to the question ,
| = 3............(i) | |
| p + 1.5 |
| = | ...........(ii) | ||
| p - 15 | 2 |
On dividing equation (i) by (ii),
| = | = | |||
| p + 1.5 | 7 | 7 |
⇒ 7p – 10.5 = 6p + 9
⇒ p = 10.5 + 9 = 19.5 kmph.
We can find the required answer with the help of given formula :
Here, t1 = 3.5, t2 = 3
Speed of Stream = 1.5 km/hr
| = | |||
| Speed of Stream | t1 - t2 |
| = | |||
| 1.5 | 3.5 - 3 |
| Speed of Boat = | = 19.5 kmph | |
| 0.5 |
