A boy can cover triple distance when swimming with the stream in a definite time period than against the stream. If speed of stream is 3km/hr, what will be speed of boy in still water?

6 km/hr

                 Downstream(D.S)      :          Upstream (U.S)

Speed:                     3                :             1

Boy : Stream= \(\frac{3\;+\;1}{2}\) : \(\frac{3\;-\;1}{2}\) = 2 : 1

Here,

1R = 3 km/hr (given)

Therefore, speed of Boy = 2 x 3 = 6 km/hr