SOLUTION: how many liters of each of 5%,10%, and 40% acid solution should be mixed together to get 18L of 20% solution, if the amount of 5% solution used to be 4L more than the amount of 10%

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Question 930267: how many liters of each of 5%,10%, and 40% acid solution should be mixed together to get 18L of 20% solution, if the amount of 5% solution used to be 4L more than the amount of 10% solution used
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
x, y, z for volume of 5,10,40 percents acid.

x%2By%2Bz=18.

Acid/volume=20%

%285x%2B10y%2B40z%29%2F18=20


Part of the description means x=y%2B10. Substituting into the other two equations:

system%28y%2B10%2By%2Bz=18%2C%285%28y%2B10%29%2B10y%2B40z%29%2F18=20%29;
Just simplify and solve this system for y and z, and then evaluate x.