A motorboat whose speed is 18 km/hr in still water takes 1 hr more to go 24 km upstream

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

Speed of Motorboat in still water= 18km/hr
Speed of stream= s km/hr
Effective Speed of motorboat when it goes upstream= 18-s
Effective speed of motorboat when is goes downstream= 18+s

Since time taken equals distance travelled divided by speed,
Time taken to tavel 24km upstream= 24/(18-s)
Time taken to travel 24km downstream= 24/(18+s)

According to the question, boat takes one hour more when it travels 24km upstream compared to downstream, so
{24/(18-s)} – {24/(18+s)} = 1

Solving this equation, you get s= 6 km/hr

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