SOLUTION: how much pure antifreeze must be added to 12 gallons of 20% antifreeze to make a 80% antifreeze solution

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Question 360172: how much pure antifreeze must be added to 12 gallons of 20% antifreeze to make a 80% antifreeze solution
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!

Hi,
Let x represent the amount of pure antifreeze that must be added
*Note: the pure antifreeze would be an 100% 'solution' of antifreeze
write as we read***
.20*12gal + 1*x = .80(12gal + x)
solve for x
.2x = .60*12gal
x = 36 gal of antifreeze needs to be added
checking our answer 2.4 + 36 = 38.4