SOLUTION: In a certain mixture of acid and water the concentration of acid is 42%. When 20 litres of mixture is replaced by water, the concentration of acid becomes 31.5%. find the volume of

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Question 987448: In a certain mixture of acid and water the concentration of acid is 42%. When 20 litres of mixture is replaced by water, the concentration of acid becomes 31.5%. find the volume of mixture in litres.
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
Most acids would need to be measured in mass. Percent concentrations could be mass/mass, mass/volume
or volume per volume. Assuming your percents are as mass/volume:

Let L be the original volume of the original mixture and be the same as the final volume
after removing v and replacing with water.

%280.42%2AL-0.42%2820%29%29%2FL=0.315

Solve for L.