Question

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.

• A. Speed of rowing in still water: 10 km/hr and the speed of the current: 5 km/hr.
• B. Speed of rowing in still water: 8 km/hr and the speed of the current: 7 km/hr.
• C. Speed of rowing in still water: 18 km/hr and the speed of the current: 12 km/hr.
• D. Speed of rowing in still water: 6 km/hr and the speed of the current: 4 km/hr.

Answer 1

Answer: (D)

Speed of rowing in still water: 6 km/hr and the speed of the current: 4 km/hr.

Let, speed of Ritu in still water be $x$ km/hr
and speed of current be $y$ km/hr

Then speed downstream $=(x+y)$ km/hr
speed upstream $=(x-y)$ km/hr

we know, $Time=\frac{Distance}{Speed}$

Then $\frac{20}{x+y}=2$ and $\frac{4}{x-y}=2$

$\Rightarrow x+y=10$ ...(1)
& $x-y=2$ ...(2)
adding both we get, $2x=12\Rightarrow x=6$
Thus using (1) $y=10-6=4$

Hence the speed of Ritu in still water is $6$ km/hr and the speed of the current is $4$ km/hr.