SOLUTION: A 40% salt solution is to be mixed with a 60% salt solution to obtain 100 gallons of a 45% salt solution. How much of each solution must be used?

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Question 344176: A 40% salt solution is to be mixed with a 60% salt solution to obtain 100 gallons of a 45% salt solution. How much of each solution must be used?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
In words:
(amount of salt in final solution)/(total gallons of final solution)
=45%
Let a = gallons of 40% solution
Let b = gallons of 60% solution
given:
Amount of salt in 40% solution = .4a
Amount of salt in 60% solution = .6b
(1) a+%2B+b+=+100
(2) %28.4a+%2B+.6b%29%2F+100+=+.45
(2) .4a+%2B+.6b+=+45
(2) 4a+%2B+6b+=+450
Multiply both sides of (1) by 4 and
subtract (1) from (2)
(2) 4a+%2B+6b+=+450
(1) -4a+-+4b+=+-400
2b+=+50
b+=+25 gallons
And, from (1)
a+%2B+b+=+100
a+%2B+25+=+100
a+=+75
75 gallons of 40% solution and 25 gallons of 60% solution must be used
check answer:
%28.4a+%2B+.6b%29%2F+100+=+.45
%28.4%2A75+%2B+.6%2A25%29%2F100+-+.45
%2830+%2B+15%29%2F100+=+.45
45%2F100+=+.45
.45+=+.45
OK