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Mathematics Question on Time Speed and Distance

A man can row 4.5 km/hr in still water and he finds that it takes him twice as long to row up as to row down the river. Find the rate of the stream.

A

1.5 km/hr

B

2 km/hr

C

2.5 km/hr

D

1.75 km/hr

Answer

1.5 km/hr

Explanation

Solution

Given that the speed in still water (u) = 4.5 km/hr
du−v\frac{d}{u-v} = 2 du+v\frac{d}{u+v}
From Equating both the equation, we get
2u - 2v = u + v
u = 3v
v = u3\frac{u}{3}
v = 4.5/3
v = 1.5 km/hr
The correct option is (A)