A man rows to a place 48 km distant and back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is?

0.5 km/hr
1 km/hr
3.5 km/hr
1.8 km/hr

Correct Answer: 1 km/hr

Explanation:

Suppose he moves 4 km downstream in H hrs.
Then, Speed downstream = 4/H km/hr
Speed upstream = 3/H km/hr
T₁ + T₂ = 14
∵ (48 x H)/4 + (48 x H)/3 = 14
⇒ 12H + 16H = 14
⇒ H = 1/2
∴ Speed downstream = 8 km/hr
Speed upstream = 6 km/hr
∴ Rate stream = (8 - 6)/2 km/hr = 1 km/hr

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