A man can row at 10 km/h in still water. If he takes total

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A man can row at 10 km/h in still water. If he takes total 5 h to go to a place 24 km away and return, then the speed of the water current is ?

1. 2 km/h
2. 3 km/h
3. 1/2 km/h
4. 1 km/h

Correct Option: A

Let speed of water current be x km/h
∴ Speed downstream = (10 + x) km/h.
Speed upstream = (10 - x) km/h
According to the question,
24/(10 + x) + 24/(10 - x) = 5
⇒ 24[10 - x + 10 + x] = 5(10² - x²)
⇒ 100 - x² = (24 x 20) / 5
⇒ 100 - x² = 96
⇒ x² = 4
⇒ x = √4 = 2km/h