BOATS and STREAMS Q46

46.	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?
	·         A. 12 kmph ·         B. 13 kmph ·         C. 14 kmph ·         D. 15 kmph

Answer: D.

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) * 1 = (x -3) * 3/2 ⇔ 2x + 6 = 3x - 9 ⇔ x = 15 kmph.