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

Given:

Ritu can row downstream 20 km in 2 hours and upstream 4 km in 2 hours.

To do: 

We have to find her speed of rowing in still water and the speed of the current.

Solution:

Let the speed of the current be $x\ km/hr$ and the speed of her rowing in still water be $y\ km/hr$.

Upstream speed $=y−x\ km/hr$

Downstream speed $=y+x\ km/hr$

$Time=\frac{speed}{distance}$

Ritu can row downstream 20 km in 2 hours.

Time taken $=\frac{20}{y+x}$

$2=​\frac{20}{y+x}$

$2(y+x)=20$

$y+x=10$.....(i)

Ritu can row upstream 4 km in 2 hours.

Time taken $=\frac{4}{y-x}$

$2=​\frac{4}{y-x}$

$2(y-x)=4$

$y-x=2$.....(ii)

Adding equations (i) and (ii), we get,

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

$2y=12$

$y=\frac{12}{2}$ 

$y=6\ km/hr$

This implies,

$6-x=2$

$x=6-2$

$x=4\ km/hr$

Therefore,

The speed of her rowing in still water is 6 km/hr and the speed of the current is 4 km/hr. 

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Updated on: 10-Oct-2022

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