Discussion of Question with ID = 070 under Boats-and-Streams

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A man can row a boat at the rate of 12 km/h in still water, and at the rate of 6 km/h against the stream. At what rate can he row down the stream?

18 km/h.

19 km/h.

17 km/h.

21 km/h.

Soln.
Ans: a

If v is the speed of the stream, 12 - v = 6, so the speed of the stream is 12 - 6 = 6 km/h. So his downstream speed would be 12 + 6 = 18 km/h.