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

Matching exercise

    
Match the items on the right to the items on the left.
STEP 1
STEP 2
STEP 3
STEP 4
STEP 5
Speed = distance/time

Let the speed of sailor in still water be ‘a’ and speed of the current be ‘b’.

The relative speed of sailor going upstream = a – b

The relative speed of sailor going downstream = a + b
Given, sailor goes 8 km downstream in 40 minutes and returns in 1 hour.



⇒ a + b = 12 ----- (1)
Also,

a – b = 8/1 = 8 ------ (2)
Adding (1) and (2).

⇒ 2a = 20

⇒ a = 10km/hr
Thus,
b = 12 – 10 = 2 km/hr

So, speed of sailor is 10 km/h and current is 2 km/h.