Question

A person rows downstream 20 km in 2 hours and upstream 4 km in 2 hours. Find man's speed of rowing in still water and the speed of the current.

Answer 1

Let man's speed of rowing in still water and the speed of the current be x km/hr and y km/hr respectively.
Then, the upstream speed = (x - y) km/hr
and the downstream speed = (x + y) km/hr
We know that
time = $\frac{distance}{speed}$
Downstream
$\Rightarrow$ $2=\frac{20}{x+y}\Rightarrow 2(x+y)=20$
$\Rightarrow$ x + y = 10 ..... (1)
Upstream
$2=\frac{4}{x-y}\Rightarrow 2(x-y)=4$
$\Rightarrow$ x - y = 2 ...... (2)
Adding (1) and (2), we get
$\Rightarrow$ 2x = 12 $\Rightarrow$ x = 6
Substituting the value of x in equation (1), we get
6 + y = 10 $\Rightarrow$ y = 4
Hence, man's speed of rowing in still water and the speed of the current are 6 km/hr and 4 km/hr respectively.