RRB Group D 1-Dec-2013 Shift 1 Solved Paper

Let the speed of the boat be x and that of the stream be y.
While travelling upstream, the speed of the boat
$=\frac{\mathit{d}}{\mathit{t}}=\frac{2}{\frac{20}{60}}=6\mathit{k}\mathit{m}∕\mathit{h}$
While travelling downstream, the speed of the boat = $\frac{\mathit{d}}{\mathit{t}}=\frac{2}{\frac{15}{60}}=8\mathit{k}\mathit{m}∕\mathit{h}$
According to the question
x + y = 8……………….i
x – y = 6………………ii
Adding both equations, we get 2x = 14
x = 7 then y = 1 km/h