Question 164484
A Chemist has a solution that is 20 % acid and 80 % water. He adds 5 liters of water to make a solution that is 15 % acid. What is the volume of the original solution.
Let x=volume of original. From info in problem we have this table:
percent acid * amount = amt acid
water .00        .80x        .00
acid 1.00        .20x        .20x   
solution           x         .20x
Now add 5 liters of water. New table looks like this:
water .00        .80x+5      .00
acid  1.00         .20x       .20x
solution .15        x+5    .15(x+5)
From Column three:
.00+.20x=.15(x+5)
20x=15(x+5)
20x=15x+75
5x=75

Professor Martin Weissman
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x=15