let rate of boat in still water be x mph
let the rate of the current be y mph
(4/3)(x+y) = 20
times 3
4x + 4y = 60
divide by 4
x + y = 15
(20/9)(x-y) = 20
times 9
20x - 20y = 180
divide by 20
x - y = 9
add them
2x = 24
x = 12
in x+y = 15 , if x = 12, then y = 3
speed of boat in still water: 12 mph
speed of current : 3 mph
Verify my answer by testing it for the given conditions.
It takes a motorboat 1 1/3 hours to go 20 miles downstream and 2 2/9 hours to return.Find the rate of the current andthe rate of the boat in still water.
1 answer
1 answer