A man can row at a speed of 15 2 km hr in still water If he takes 4 times as long to row a distance ...........

Quant (SSC) Boats and Streams

A man can row at a speed of 15/2 km/hr in still water. If he takes 4 times as long to row a distance upstream as to row the same distance downstream, then the speed of stream (in km/hr) is

3.75

4.5

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Explanation:

Let the speed of stream be x kmph
∴ Rate upstream = 15/2 - x
And rate downstream = 15/2 + 2
Let's also assume the time taken in downstream and upstream is 1 hr and 4 hrs respectively.
We know that, Distance = Speed × Time
∴ (15/2 + X) x 1
= (15/2 - X) x 4
⇒ (15 + 2x) = (60 – 8x)
⇒ 10x = 45
∴ x = 45/10 = 9/2 = 4.5 kmph