Question 98496
A radiator contains 6 liters of 25% antifreeze solution. How much should be drained and replaced with pure antifreeze to produce a 33% antifreeze solution? 
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Note: Keep track of the active ingredient.
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Start: 25%*6 liters = (3/2)liters of active
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You subtract x liters but it is still 25% active:
You now have: (3/2)-(x/4) active;
You add x amount of 100% active:
You now have (3/2)-(x/4)+x active
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That amount of active is 33% of the 6 liters you now have:
EQUATION:
(3/2)-(x/4)+x = 33%*6
(3/2) + (3/4)x = 2
(3/4)x = 1/2
x = (1/2)(4/3)
x = 2/3 liters
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That is the amount of 100% alcohol you should add.
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Cheers,
Stan H.