Question

a boat takes 2 hrs to go 4 km down the stream and return in 4 hrs find the speed of the boat in still water and speed of the stream

Answer 1

 Lets speed of boat = x km/hr
and speed of current = y km/hr

So while going upstream speed of man = x-y km/hr
and while going downstream =  x+y km/hr

A/Q : 4/x+y = 2  ⇒ 2x + 2y = 4 ⇒ x+y = 2  ⇒ y = 2-x ..........(1)

And  4 /x-y = 4 ⇒ x-y = 1 from (1)

x-(2-x) = 1 ⇒ 2x - 2 = 1  ⇒ x = 3/2    and so y = 1/2

Hence speed of boat = 1.5 km/hr (in still water)

speed of current = 0.5 km/hr

Hope this helps.