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You can put this solution on YOUR website!
\n" ); document.write( "Tutor @ikleyn solves the problem by the traditional algebraic method, using two equations and two unknowns. This is a good example of how to use algebra to solve problems; you should understand it.
\n" ); document.write( "Tutor @josgarithmetic shows how to solve the problem using his/her favorite formula for solving mixture problems, involving a whole bunch of variables. If you like to memorize ugly formulas (generally without understanding WHERE those formulas come from) then you can use that method.
\n" ); document.write( "But if a formal algebraic solution is not required, here is a way you can solve the problem mentally in a few seconds:
\n" ); document.write( "(1) 30% is \"twice as close to 20% as it is to 50%\". (to help you see this, picture the three percentages 20, 30, and 50 on a number line....)
\n" ); document.write( "(2) Therefore, the mixture must contain twice as much of the 20% alcohol as it does the 50% alcohol.
\n" ); document.write( "9 gallons total, with twice as much 20% alcohol as 50% alcohol means 6 gallons of 20% and 3 gallons of 50%.
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