document.write( "Question 911345: How much pure copper must be added to 50 kg of an alloy containing 12% copper to raise the copper content to 21%? \n" ); document.write( "

Algebra.Com's Answer #553039 by josmiceli(19441) $\"\"$ $\"About$

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Let $\"+x+\"$ = kg of pure copper to be added
\n" ); document.write( " $\"+.12%2A50+=+6+\"$ kg of copper in 12% alloy
\n" ); document.write( "---------------------
\n" ); document.write( " $\"+%28+6+%2B+x+%29+%2F+%28+50+%2B+x+%29+=+.21+\"$
\n" ); document.write( " $\"+6+%2B+x+=+.21%2A%28+50+%2B+x+%29+\"$
\n" ); document.write( " $\"+6+%2B+x+=+10.5+%2B+.21x+\"$
\n" ); document.write( " $\"+.79x+=+4.5+\"$
\n" ); document.write( " $\"+x+=+5.696+\"$
\n" ); document.write( "5.696 kg of pure copper must be added
\n" ); document.write( "------------------
\n" ); document.write( "check:
\n" ); document.write( " $\"+%28+6+%2B+x+%29+%2F+%28+50+%2B+x+%29+=+.21+\"$
\n" ); document.write( " $\"+%28+6+%2B+5.696+%29+%2F+%28+50+%2B+5.696+%29+=+.21+\"$
\n" ); document.write( " $\"+11.696+%2F+55.696+=+.21+\"$
\n" ); document.write( " $\"+11.696+=+.21%2A55.696+\"$
\n" ); document.write( " $\"+11.696+=+11.696+\"$
\n" ); document.write( "OK \n" ); document.write( "

\n" );