A motor boat whose speed is 18 km/h in still water takes 1 hour more to go 24 km upstream

than to return downstream to the same spot. Find the speed of the stream.

Given, speed of the boat in still water = 18 km/hr.

Let the speed of the stream be x km/hr.

Speed of the boat upstream = Speed of boat in still water – Speed of the stream

∴ Speed of the boat upstream = ( 18 – x ) km/hr

Speed of the boat downstream = Speed of boat in still water + Speed of the stream

∴ Speed of the boat downstream = ( 18 + x ) km/hr

Time of upstream journey = Time for downstream journey + 1 hr

⇒ 48x = 324 – x2 

 x2 + 48x – 324 = 0

 x = 6  (Speed of the stream cannot be negative)

Thus, the speed of stream is 6 km/hr.

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