Ram can row a boat in still water at the rate of 6 km/hr. He finds that it takes him twice as long to row upstream of a river as to row downstream of the same river, then the speed of the current of the river is

2 km/hr

The correct answer is Option (4) → 2 km/hr **

Let speed of current = $v$ km/hr.

Speed upstream = $6 - v$

Speed downstream = $6 + v$

Given:

Time upstream = 2 × Time downstream

Since time = $\frac{d}{\text{speed}}$ and distance is same:

$\frac{1}{6 - v} = 2 \cdot \frac{1}{6 + v}$

Cross-multiply:

$6 + v = 2(6 - v)$

$6 + v = 12 - 2v$

$3v = 6$

$v = 2$

The speed of the current is 2 km/hr.