Question 271287
How many liters of a 40% antifreeze solution must be mixed with 5 liters of a 70% antifreeze solution to make a mixture that is 60% antifreeze? 
I can't figure out how to set this up.

mixture A + mixture B = mixture C
OR
% in A * A + % in B * B = % in C * C
40% * A + 70% * B = 60% * C
A = x, B = 5 liters, C = 5+x liters
0.40x + 0.70 * 5 = 0.60(5+x)
0.40x + 3.5 = 3 + 0.60x
0.5 = 0.20x
2.5 liters = x