SOLUTION: How much pure (100%) antifreeze must be added to 4 quarts of 20% antifreeze solution to produce a 25% antifreeze solution?

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Question 72854: How much pure (100%) antifreeze must be added to 4 quarts of 20% antifreeze solution to produce a 25% antifreeze solution?
Found 2 solutions by checkley75, blfaust:
Answer by checkley75(3666) About Me  (Show Source):
You can put this solution on YOUR website!
20*.2+X=(20+X).25
4+X=5+.25X
X-.25X=5-4
.75X=1
X=1/.75
X=1.333 QUARTS OF 100% NEEDS TO BE ADDED.

Answer by blfaust(5) About Me  (Show Source):
You can put this solution on YOUR website!
You would need to add .2666666 quarts of pure (100%)anitfreeze to 4 quarts of a 20% solution to make it a 25% solution.
In 4 quarts, a 20% solution is .8 quarts of antifreeze. 4*(.2)=y => .8=y
That can be rewritten as %28.8%29%2F4+=+.2
To solve set up as %28.8%2Bx%29%2F%284%2Bx%29=.25