Ritu can row downstream 20 km in 2 hours, and uptream 4 km in 2 hours. Find her speed of rowing in still water and the speed of the current.
Let us assume the speed of boat in still water is x and speed of current is y.
Hence, downstream speed = x + y and upstream speed = x – y
Case (i): time=distancespeed [downstream]
2=20x+y
2 (x+y) = 20
2x + 2y = 20
x + y = 10 -------(i)
Case (ii): time=distancespeed [upstream]
2=4x−y
2(x -y) = 4
x -y = 2 -------(ii)
Now, add eq.(i) ad eq. (ii);
2x = 12
x = 6
Substituting, the value of x in eq.(i)
x + y = 10
y = 10 - 6 = 4
Thus, speed of rowing in still water = 6 km/hr and speed of current = 4 km/hr