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

Solution(By Examveda Team)

Let downstream speed be D and Upstream speed be U. Then
$$\eqalign{ & {\frac{{48}}{U} + \frac{{72}}{D}} = 12\,.\,.\,.\,.\,.\,.\,.\left( 1 \right) \cr & {\text{and}} \cr & {\frac{{72}}{U} + \frac{{48}}{D}} = 13\,.\,.\,.\,.\,.\,.\,.\left( 2 \right) \cr} $$
On solving the equation (1) and (2), we get
D = 12 kmph and
U = 8 kmph
Thus, speed of the current
$$ = \frac{{D - U}}{2} = \frac{4}{2} = 2\,{\text{kmph}}$$