Q. 144.1( 16 Votes )

A motorboat whose

Answer :

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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