Question

Rahul can row a certain distance downstream in 6 hours and return the same distance in 9 hours.If the speed of Rahul in still water is 12 km/hr find the speed of the stream.

• A. 2 km/hr
• B. 2.4 km/hr
• C. 3 km/hr
• D. Data inadequate

Answer 1

Answer: (B)

2.4 km/hr

Answer 2

Let take the speed of Rahul be u, the speed of stream be v and the distance travelled be d.
$\frac{d}{u+v}$ = 6 – Equation 1
$\frac{d}{u-v}$ = 9 – Equation 2
Given the speed of Rahul (u) = 12 km/hr
From Equation 1 we have,
6u + 6v = d
From Equation 2 we have,
d = 9u - 9v
By equating both the equation we have,
6u + 6v = 9u - 9v
3u = 15v
u = 5v
The value of u is given i.e. 12
12 = 5v
So the value of v = $\frac{12}{7}$ = 2.4 km/hr
The correct option is (B)