Question

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

Answer 1

Let speed of Ritu in still water $=xkm/h$

Speed of stream $=ykm/h$

Then downstream speed of Ritu $=(x+y)km/h$

Upstream speed of Ritu $=(x-y)km/h$

$Speed=\frac{Distance}{time}⟹time=\frac{Distance}{Speed}$

According to question,

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

$⟹x+y=10$ .... (1)

Also,

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

$⟹x-y=2$ ..... (2)

Adding (1) and (2), we get

$2x=12$

$⟹x=6$

From (1), we get

$6+y=10$

$y=4$

Speed of Ritu in still water $=6km/h$

Speed of stream $=4km/h$