SOLUTION: how many quarts of pure antifreeze must be added to 4 quarts of a 10% antifreeze solution to obtain a 20% antifreeze solution?

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Question 266828: how many quarts of pure antifreeze must be added to 4 quarts of a 10% antifreeze solution to obtain a 20% antifreeze solution?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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how many quarts of pure antifreeze must be added to 4 quarts of a 10% antifreeze solution to obtain a 20% antifreeze solution?
:
Let x = amt of pure antifreeze required
:
Write a decimal equiv mixture equation (pure antifreeze is 100% or 1x)
.10(4) + x = .20(x + 4)
.4 + x = .2x + .8
x - .2x = .8 - .4
.8x = .4
x = .4%2F.8
x = .5, half a quart of pure antifreeze required