how many liters of a 40% and 25% concentration must be mixed to obtain 150 liters of a 39% solution
.4x + .25(150-x) = .39(150)
Multiply both sides by 100
40x + 25(150-x) = 39(150)
40x + 3750 - 25x = 5850
15x = 2100
x = 140
140L of 40% solution, plus 10L of 25% solution gives 150L of 39% solution
(0.4 * 140) + (0.25 * 10) = 0.39 * 150
56 + 2.5 = 58.5