Question

A boat takes 2 hours to go 40km down the stream and it returns in 4 hours. Find the speed of the boat in still water and the speed of the stream

Answer 1

let speed of boat in still water be x km/h
let the speed of the current be y km/h

time to go with the current is 2 hrs
40/(x+y) = 2
2x + 2y = 40
x + y = 20

time to go against the current is 4 hrs
40/(x-y) = 4
4x - 4y = 40
x - y = 10

add the two equations:
2x = 30
x = 15
sub into the first:
15 + y = 20
y = 5

the boat can go 15 km/h and the current is 5 km/h

Answer 2

Thanks for it it was bit tricky.