<PRE><B>Question 516393</B>
500gallon heating tank at 20% ethanol. You need it to be a 40% ethanol solution. You can only add 100% ethanol.----
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Equation: 
eth + eth = eth
0.20*500 + 1.00x = 0.40(500+x)
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Multiply thru by 100 to get:
20*500 + 100x = 40*500 + 40x
60x = 20*500
x = (1/3)500
x = 166 2/3 gallong (amt. of 100% ethonol to be added)
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Cheers,
Stan H.
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