A motorboat whose speed in still water is 18 km/hr takes 1 hour more to go 24 km upstream that to return downstream to the same spot. Find the speed of the stream.

Time = Distance/speed


Given, motorboat whose speed in still water is 18 km/hr takes 1 hour more to go 24 km upstream that to return downstream to the same spot.


Let the speed of stream be ‘a’ km/hr.


Relative speed of boat going upstream = 18 – a km/hr


Relative speed of boat going downstream = 18 + a km/hr



⇒ 24(18 + a – 18 + a) = -a2 + 324


⇒ a2 + 48a – 324 = 0


⇒ a2 + 54a - 6a – 324 = 0


⇒ a(a + 54) – 6(a + 54) = 0


⇒ (a – 6)(a + 54) = 0


⇒ a = 6 km/hr

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