SOLUTION: How many liters of 70% alcohol and 40% solution must be mixed to obtain 6 liters of 60% alcohol solution?

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Question 1095387: How many liters of 70% alcohol and 40% solution must be mixed to obtain 6 liters of 60% alcohol solution?
Found 2 solutions by josgarithmetic, addingup:
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
x and y liters of 40% and 70%

system%2840x%2B70y=60%2A6%2Cx%2By=6%29

4x%2B7y=36
highlight_green%284x%2B7%286-x%29=36%29--------equation in ONE variable
-
4x%2B42-7x=36
-3x=36-42
3x=6
x=2
-
2 liters of 40% alcohol
4 liters of 70% alcohol

Answer by addingup(3677) About Me  (Show Source):
You can put this solution on YOUR website!
0.7x + 0.4(6 - x) = 0.6(6)
0.7x + 2.4 - 0.4x = 3.6
0.3x / 1.2
x = 4 you need 4 liters of the 70% solution and
6 - 4 = 2 liters of the 40% solution