A boat covers a certain distance downstream in 1 hour, while it comes back in 1½ hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?

12 kmph
13 kmph
14 kmph
15 kmph
None of these

Correct Answer: 15 kmph

Explanation:

Let the speed of the boat in still water be x kmph. Then,

Speed downstream = (x + 3) kmph,

Speed upstream = (x - 3) kmph.

∴ (x + 3) x 1 = (x - 3) x	3
	2

⟹ 2x + 6 = 3x - 9

⟹ x = 15 kmph.

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