A boatman rows 30 km downstream in exactly the same time as he takes to row 18 km upstream. If the stream flows at 3 km/h, his speed in still water (in km/h) is:

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Accepted Answer

12. Equal times over the two legs mean the distances are in the ratio of the speeds: 30/(v + 3) = 18/(v − 3) → 30v − 90 = 18v + 54 → 12v = 144 → v = 12 km/h. (Check: downstream 15 km/h covers 30 km in 2 hours and upstream 9 km/h covers 18 km in the same 2 hours.)

A boatman rows 30 km downstream in exactly the same time as he takes to row 18 km upstream. If the stream flows at 3 km/h, his speed in still water (in km/h) is:

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