Question

A sailor goes 8km downstream in 40 mins and returns to the starting point in 1 hr. Find the speed of the sailor in still water and speed of the current.

Answer 1

Let x be the speed of the sailor in still water. 
and y be the speed of the water current. 

While going downstream, the speed is (x + y) = 8 / (40/60) ------ (distance / time) 
x + y = 12 -------- (1) 
While going upstream, the speed is (x - y) = 8/1 
x - y = 8 ---------------------- (2) 
Adding (1) and (2) we get 2 x = 20 ==> x = 10 km/h 
From (1) or (2) , substituting x = 10, ==> y = 2 km/h 

So, the speed of sailor = 10 km/h and speed of water current = 2 kmh

Answer 2

Answer:

⇒ x + y = 12  

⇒ x - y = 8  

--------------  

⇒ 2x = 20,  

⇒ 2y = 4  

⇒ x = 10,  

⇒ y = 2  

⇒Speed of stream = 2 kmph, Speed of boat = 10 kmph