Question

A boatman rows to a place 45 km distant and back in 20 hours. He finds that he can row 12 km with the stream in same time as 4 km against the stream . Find the speed of the stream.

• A. 3 km/hr
• B. 2.5 km/hr
• C. 4 km/hr
• D. Cannot be determined

Answer 1

Answer: (A)

3 km/hr

Answer 2

Let's take the speed of the boat be u and that of stream be v.

$\frac{12}{u}+v=\frac{3}{u-v}$

$4u-4v=u+v$
$3u=5v$

$\frac{45}{u+v}+\frac{45}{u-v}=20$

By putting value of u in above equation and after solving the equation, we get
v [speed of stream] = 3 km/hr
The correct option is (A)