A scientist needs 10 litera of a 20% acid solution for an experiment but she has only 5% solution and a 40% solution. To the nearest tenth of a liter, how many liters of the 5% and the 40% solutions should she mix to get the solution she needs?




x = liters of 5% solution
y = liters of 40% solution
The scientist wants 10 L total of a 20% solution, so
x + y = 10
0.05 x + 0.40 y = 0.20 (x + y) = 2
From the first equation,
y = 10 - x
Substitute this into the second equation and solve for x :
0.05 x + 0.40 (10 - x) = 2
0.05 x + 4 - 0.40 x = 2
2 = 0.35 x
x ≈ 5.714 L
Solve for y :
y = 10 - x
y ≈ 4.286 L