Question

A swimming pool contains x (less than 0.02) grams of chlorine per cubic meter. the pool measures 5 meters by 50 meters and is 2 meters deep. some water will be drained and replaced by water contain 5 grams of chlorine per cubic meter. how much water should be drained so the pool ends up with 0.02 grams of chlorine per cubic meter.

Answer 1

The solution for this problem would be:(10 - 500x) / (5 - x) 
so start by doing: 
x(5*50*2) - xV + 5V = 0.02(5*50*2) 
500x - xV + 5V = 10 
V(5 - x) = 10 - 500x 
V = (10 - 500x) / (5 - x) 
(V stands for the volume, but leaves us with the expression for x)