SOLUTION: How many liters of a 20% acid solution must be added to 100 liters of a 50% acid solution to get a 40% solution?

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Question 410167: How many liters of a 20% acid solution must be added to 100 liters of a 50% acid solution to get a 40% solution?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = liters of 20% solution needed
given:
.2a = liters of acid in 20% solution
.5%2A100+=+50 = liters of acid in 50% solution
%28.2a+%2B+50%29+%2F+%28100+%2B+a%29+=+.4
.2a+%2B+50+=+.4%2A%28100+%2B+a%29
.2a+%2B+50+=+40+%2B+.4a
.2a+=+10
a+=+50
50 liters of 20% solution must be added
check:
%28.2%2A50+%2B+50%29+%2F+%28100+%2B+50%29+=+.4
60%2F150+=+.4
60+=+60
OK