Problema Solution
Officials begin to release water from a full man-made lake at a rate that would empty the lake in 4 weeks, but a river that can fill the lake in 15 weeks is replenishing the lake at the same time. How long does it take to empty the lake?
Answer provided by our tutors
let
x = the number of weeks for the lake to empty
empty rate - fill rate = together empty rate
1/4 - 1/15 = 1/x multiply both sides by 60x
15x - 4x = 60
11x = 60
x = 60/11
x = 5 5/11 weeks = 5 weeks 3.2 days
it takes 5 weeks 3.2 days to empty the lake.