Question

Rohit can row downstream 32 km in 4 hours and upstream 4km in 1 hour. Find his speed in still water and the speed of the current.

• A. 6 km/hr, 2 km/hr
• B. 4 km/hr, 4 km/hr
• C. 20 km/hr, 4 km/hr
• D. 4 km/hr, 2 km/hr

Answer 1

The correct option is A

6 km/hr, 2 km/hr

Let speed of Rohit rowing in still water = x km/hr
and speed of current = y km/hr. Then,
Speed downstream = (x + y) km/hr
Speed upstream = (x - y) km / hr
We know that,
$Time=\frac{Distance}{Speed}$

$4=\frac{32}{x+y}and1=\frac{4}{x-y}$

$\Rightarrow x+y=8\cdots \left(1\right)$
$\Rightarrow x-y=4\cdots \left(2\right)$
On adding (1) and (2), we get
2x = 12
$\Rightarrow$ x = 6
On substituiting x = 6 in (1), we get
6 + y = 8
$\Rightarrow$ y = 2
$\therefore$ The rowing speed in still water is 6 km/hr and the speed of current is 2 km/hr.