### A boat covers 48 km upstream and 72 km downstream in 12 hours, while it covers 72 km upstream and 48 km downstream in 13 hours The speed of stream is :

A. 2 kmph B. 2.2 kmph C. 2.5 kmph D. 4 kmph Answer: Option A
Let downstream speed be D and Upstream speed be U. Then, $\frac{48}{U}+\frac{72}{D}=12 \ldots \ldots(1)$ and $\frac{72}{U}+\frac{48}{D}=13 \ldots . .(2)$ On solving the equation (1) and (2), we get D = 12 kmph and U = 8 kmph Thus, speed of the current $=\frac{D-U}{2}=\frac{4}{2}=2 \mathrm{kmph}$