SOLUTION: Pure acid is to be added to a 10% acid solution to obtain 81 L of a 20% acid solutions. What amounts of each should be used?

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Question 992498: Pure acid is to be added to a 10% acid solution to obtain 81 L of a 20% acid solutions. What amounts of each should be used?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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Pure acid is to be added to a 10% acid solution to obtain 81 L of a 20% acid solutions.
What amounts of each should be used?
:
let a = amt of pure acid to be used
then
(81-a) = amt of 10% solution required
:
A typical mixture equation
a + .10(81-a) = .20(81)
a + 8.1 - .10a = 16.2
a - .1a = 16.2 - 8.1
.9a = 8.1
a = 8.1/.9
a = 9 liters of pure acid
then
81- 9 = 72 liters of 10% solution