Question

A sailor goes 8 km downstream in 40 minutes and returns in 1 hour.Find the speed of the sailor in still water and the speed of the current.

Answer 1

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

The speed of boat (upstream) = (x - y) km/hr.

The speed of boat (downstream) = (x + y) km/hr.

Now,

A.T.Q.

(1) 8 / (x + y) = 40 / 60
(Since, Time = Distance / Speed)

⇒ x + y = 12 ------------ (1)

(2) 8/ (x - y) = 1
(Since, Time = Distance / Speed)

⇒ x - y = 8 ---------------- (2)

On adding (1) and (2),

⇒ x + y + x - y = 12 + 8

⇒ 2 x = 20

⇒ x = 10

By (1)

10 + y = 12

⇒ y = 2.

Ans :- The speed of sailor in still water is 10 km / hr.

The speed of stream is 2 km / hr.