Question 631713
Solution A
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Amount = x 
Concentration =40% =0.4


Solution B
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Amount = 12-x 
Concentration =60% = 0.6

Mixture
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Amount =12 
Concentration =45%=0.45

[Amount Solution A * Concentration A] + [Amount Solution B * Concentration of B] = [Amount of Mixture *Concentration of Mixture]
(x)(0.4)+(12-x)(0.6)=(12)(0.45)
0.4x+7.2-0.6x=5.4
-0.2x+7.2=5.4
-0.2x=-1.8
-0.2x/-0.2=-1.8/-0.2
x=9



Solution A
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Amount = x = 9 gallons
Concentration =40% =0.4
Solution B
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Amount = 12-x = 12-9 = 3 gallons
Concentration =60% = 0.6



9 gallons of the 40% solution and 3 gallons of the 60% solution should be mix together to obtain 12 gallons of 45% solution?