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.
Speed = distance/time
Let the speed of sailor in still water be ‘a’ and speed of the current be ‘b’.
Relative speed of sailor going upstream = a – b
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