Question

A man can row a boat downstream 20 km in 2 hours and upstream 4 km in 2 hours. Find his speed of rowing in still water. Also find the speed of the stream.

Answer 1

Let the speed of the boat in still water be x km/hr and speed of the stream be y km/hr.

∴ Relative Speed of boat in upstream = (x – y) km/hr and Relative speed of boat in downstream = (x + y) km/hr

According to the question,

`20/(x + y) = 2`

⇒ x + y = 10   ...(i)

And `4/(x - y) = 2`

⇒ x – y = 2   ...(ii)

On adding equations (i) and (ii), we get

2x = 12

⇒ x = 6

Putting the value of x is equation (i),

6 + y = 10

⇒ y = 10 – 6

⇒ y = 4

Speed of a boat in still water = 6 km/hr and speed of the stream = 4 km/hr.