Question 655944
The radiator in Natalie's car contains 6.3 L of antifreeze and water. This mixture is 30% antifreeze. How much of this mixture should she drain and replace with pure antifreeze so that there will be a mixtuure of 50% antifreeze? 
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Equation:
alcohol - alcohol + alcohol = alcohol
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0.30*6.3 - 0.30x + 1.00x  = 0.50*6.3
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30*6.3 - 30x + 100x = 50*6.3
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70x = 20*6.3
x = (2/7)6.3
x = 2*0.9
x = 1.8 L (amt. to remove and replace)
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Cheers,
Stan H.