Question 708615: If a scientist has 35% acid solution and 20% acid solution and she needs 3 liters of 25% acid solution write and solve a linear equation of how much of each solution she should use.
Answer by josgarithmetic(39625)   (Show Source):
You can put this solution on YOUR website! If you want filling in with values, then for a of the 20% acid and b of the 35% acid, you can make these:
 and 
From the rational equation, multiply left and right by 3, and also divide both sides by 5 (seeing that all terms include a multiple of 5):
4a+7b=3*5,
We have this adjusted system to solve for a and b:
From that, you have a choice of methods. Substitution, elimination, or simple matrix operations if you wish to.
Trying substitution, gives us  ;
Put into  , and.....
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