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

The Correct Option is A

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)