SOLUTION: how many quarts of pure antifreeze must be added to 9 quarts of a 20% antifreeze solution to obtain a 30% antifreeze solution?

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Question 772180: how many quarts of pure antifreeze must be added to 9 quarts of a 20% antifreeze solution to obtain a 30% antifreeze solution?
Answer by modi.kk91(20)   (Show Source): You can put this solution on YOUR website!
let pure antifreeze=100%
quarts=x

x*100%+9*20%=30%(X+9)
100x+180=30x+270

100x-30x=270-180
70x= 90

x=90/70

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