document.write( "Question 1117131: How many kilograms of sand must be added to 300 kg of a mixture of sand and cement containing 40% cement to produce a mixture which will be 75% sand? \n" ); document.write( "
Algebra.Com's Answer #732147 by greenestamps(13200)\"\" \"About 
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\n" ); document.write( "You have received two responses to your question, both using an algebraic solution using an equation for the amount of sand in the mixture:

\n" ); document.write( "\"x kg of sand, plus 60% of 300 kg of mixture which is 60% sand, equals 75% of (x+300) kg of sand\"

\n" ); document.write( "This of course is a valid approach to the problem. However, when one of the ingredients being mixed is 100% one thing and 0% the other, I find it easier to think in terms of the ingredient that is NOT being added.

\n" ); document.write( "For this problem, you start with 300 kg of a mixture which is 40% cement and 60% sand, and you are adding only sand to end up with a mixture that is 75% sand and only 25% cement.

\n" ); document.write( "(1) The cement in the original mixture is 40% of 300 kg, or 120 kg.
\n" ); document.write( "(2) When the additional sand is added to the mixture, that 120 kg is now only 25% of the mixture.
\n" ); document.write( "(3) So the total amount of mixture must now be 120/.25 = 480 kg.
\n" ); document.write( "(4) So the amount of sand that was added was 480-300 = 180 kg.
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