A motor boat whose speed is 15 km/hr in still water goes 36 km upstream and comes back to the starting point in 5 hours . Find the speed of the stream - Mathematics and Science MCQ UPTET Paper 2 (Maths & Science) 2026 | ExamTest.live

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A motor boat whose speed is 15 km/hr in still water goes 36 km upstream and comes back to the starting point in 5 hours . Find the speed of the stream.

Solution & Step-by-step Explanation

Let the speed of the stream be x km/hr .Upstream speed = 15 - x Downstream speed = 15 + x The total round-trip time taken is 5 hours over a distance of 36 km : \frac{36}{15 - x} + \frac{36}{15 + x} = 5 36 [\frac{( 15 + x ) + ( 15 - x )}{( 15 - x ) ( 15 + x )}] = 5 36 [\frac{30}{225 - x ^{2}}] = 5 \frac{1080}{225 - x ^{2}} = 5 1080 = 5 (225 - x^{2}) = 1125 - 5 x^{2} 5 x^{2} = 1125 - 1080 = 45 x^{2} = 9 ⟹ x = 3 km/hr

Try it yourself before checking the explanation above.

A motor boat whose speed is 15 km/hr in still water goes 36 km upstream and comes back to the starting point in 5 hours . Find the speed of the stream.

5 km/hr

10 km/hr

Can't determine

3 km/hr

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