Question 271245
How many liters of water containing 5 grams of salt per liter must be combined with x liters of water which contains y grams [y is less than 2] of salt per liter to yield a solution with 2 grams of salt per liter. 
Equation in x and y=?

let L = number of liters of 5 g/L solution

5L + yx = 2(L+x)
5L + yx = 2L + 2x
3L + yx = 2x
3L = 2x - yx = x(2-y)
3L / (2-y) = x (this is x)
L = x(2-y) / 3 (this is L)
yx = 2x - 3L
y = (2x - 3L)/x (this is y)

L max when y=0 --> L = x(2-0) / 3 = 2x / 3
L min when y=2 --> L = x(2-2) / 3 = 0

0 < L < (2x)/3