Question

Ritu can row downstream $20km$ in $2hours$ and upstream $4km$ in $2hours$. Find her speed of rowing in still water and the speed of current.

Answer 1

Let the speed of stream be $y$ km/h and speed of boat in still water be $x$ km/h

So, the speed of boat in downstream be $(x+y)$ km\h and speed of boat in upstream be $(x-y)$ km/h

According to question-

$\frac{20}{x+y}=2$

$\Rightarrow x+y=10$ ......(1)

And

$\frac{4}{x-y}=2$

$\Rightarrow x-y=2$ ......(2)

Adding equation (1) and (2), we get

$\Rightarrow x+y+x-y=10+2$

$\Rightarrow 2x=12$

$\Rightarrow x=6$ km/h

Now, substituting this value of $x$ in equation (1), we get

$6+y=10$

$y=4$ km/h.

Hence, this is the required solution.