In a swimming race, you find that a swimmer can swim downstream (with the current) in a river, 2 miles in 40 minutes, & upstream (against the current) 2 miles in 60 minutes. How long would it take the swimmer to swim a mile in still water?

Answer 1

40 min = 2/3 hr
60 min = 1 hr

let the speed of the swimmer in still water be x mph
let the speed of the river be y mph

(2/3)(x+y) = 2
2(x+y) = 6
x + y = 3

1(x-y) = 2
x - y = 2

add them
2x = 5
x = 2.5 , then by mental math, y = .3

his rate in still water is 2.5 miles in 60 minutes
so to do one mile would take 60/2.5 or 24 minutes