Question
A boat travels 36 km downstream in 3 hours and the same distance upstream in 6 hours. Find the speed of the boat in still water and the speed of the stream.
Solution
Downstream speed = 36/3 = 12 km/h Upstream speed = 36/6 = 6 km/h Let b = speed of boat in still water, s = speed of stream. Downstream: b + s = 12 Upstream: b − s = 6 Add: 2b = 18 ⇒ b = 9 km/h Then: 9 + s = 12 ⇒ s = 3 km/h Answer: Boat speed = 9 km/h; Stream speed = 3 km/h.
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