Question 945758
 officials begin to empty a man made lake at a rate that would empty the lake in 18 weeks
 but a river that can fill the lake in 30 weeks is replenishing the lake at the same time,
 how long would it take to empty the lake
:
let t = time to empty the lake in this scenario
let the completed job = 1 (an empty lake)
:
{{{t/18}}} - {{{t/30}}} = 1
Multiply equation by 90
90*{{{t/18}}} - 90*{{{t/30}}} = 1(90)
Cancel the denominators
5t - 3t = 90
2t = 90
t = 45 weeks to empty the lake