SOLUTION: How many liters of 20% solution and how many liters of 70% solution must be combineed to produce five liters of 40% solution?

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Question 227475: How many liters of 20% solution and how many liters of 70% solution must be combineed to produce five liters of 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
Let b= liters of 70% solution needed
%28.2a+%2B+.7b%29%2F5+=+.4
.2a+%2B+.7b+=+2
(1) 2a+%2B+7b+=+20
(2) a+%2B+b+=+5
Multiply both sides of (2) by 2
and subtract from (1)
(1) 2a+%2B+7b+=+20
(2) -2a+%2B+-2b+=+-10
5b+=+10
b+=+2
and, since
a+%2B+b+=+5
a+=+5+-+b
a+=+5+-+2
a+=+3
2 liters of 20% solution and 3 liters of 70%
solution are needed