document.write( "Question 1203535: You need to strengthen a 22% alcohol solution with a pure alcohol solution to obtain a 70% solution. How much pure alcohol should you add to 100 milliliters of the 22% solution? \n" ); document.write( "
Algebra.Com's Answer #839176 by greenestamps(13200)\"\" \"About 
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\n" ); document.write( "The standard algebraic solution looks something like this:

\n" ); document.write( "100 ml of 22% alcohol, plus x ml of 100% alcohol, yields (100+x) ml of 70% alcohol.

\n" ); document.write( "\".22%28100%29%2B1.00%28x%29=.70%28100%2Bx%29\"
\n" ); document.write( "\"22%2Bx=70%2B.7x\"
\n" ); document.write( "\".3x=48\"
\n" ); document.write( "\"x=48%2F.3=160\"

\n" ); document.write( "ANSWER: 160 ml

\n" ); document.write( "Here is an alternative, informal method which often makes reaching the answer easier.

\n" ); document.write( "Picture a number line showing the three percentages -- 22, 70, and 100. Calculate that 70 is 48/78 of the way from 22 to 100 (22 to 70 is a difference of 48; 22 to 100 is a difference of 78).

\n" ); document.write( "That fraction 48/78 means the two ingredients must be mixed in the ratio 48:(78-48) = 48:30 = 8:5. Since 70% is closer to 100% than to 22%, the larger portion must be the 100% alcohol. Then we have the proportion

\n" ); document.write( "\"8%3A5=x%3A100\"
\n" ); document.write( "\"5x=800\"
\n" ); document.write( "\"x=160\"

\n" ); document.write( "And again of course the answer is 160 ml.

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