Answer:
30%: 35 liters
50%: 35 liters
Step-by-step explanation:
The desired concentration is halfway between the concentrations of available solutions, so the mixture will be equal amounts of each.
35 liters of 30% acid and 35 liters of 50% acid must be used
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If you want to write an equation, it usually works well to let the variable represent the amount of the most concentrated constituent: 50% acid. Then the amount of acid in the final mix is ...
0.50x +0.30(70 -x) = 0.40(70)
0.20x +21 = 28 . . . . simplify
0.20x = 7 . . . . . . . . . subtract 21; next, divide by 0.20
x = 35 . . . . . . amount of 50% solution (liters)
70-x = 35 . . . amount of 30% solution (liters)
