Math Algebra , high school
posted by Gina .
A biologist has three salt solutions: some 5% solution, some 15% solution, and some 25% solution. She needs to mix some of each to get 50 liters of 20% solution. She wants to us twice as much of the 5% solution as the 15% solution. How much of each solution should she use? How do I set it up using 3 varibles

x+y+z = 50
x = 2y
.05x + .15y + .25z = .20(50)
(x,y,z) = (10,5,35)