Question 529818
A tank contains 20 gallons of antifreeze solution.  When it is full, it contains 15% antifreeze.  How many gallons must be replaced by an 80% antifreeze solution to get 20 
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Equation:
alcohol - alcohol + alcohol = alcohol
0.15*20 - 0.15x + 0.80x = ?*20
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You post does not state the % of alcohol in the final solution.
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cheers,
Stan H.