document.write( "Question 524950: The average of three numbers is 12 and that of first two number is 9. Find the third number? \n" ); document.write( "

Algebra.Com's Answer #347987 by josmiceli(19441) $\"\"$ $\"About$

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Let the numbers be $\"a\"$ , $\"b\"$ , and $\"c\"$
\n" ); document.write( "given:
\n" ); document.write( "(1) $\"+%28a+%2B+b+%2B+c%29%2F3+=+12+\"$
\n" ); document.write( "(2) $\"+%28a+%2B+b%29%2F2+=+9+\"$
\n" ); document.write( "--------------
\n" ); document.write( "(2) $\"+%28a+%2B+b%29%2F2+=+9+\"$
\n" ); document.write( "(2) $\"+a+%2B+b+=+18+\"$
\n" ); document.write( "Substitute this back into (1)
\n" ); document.write( "(1) $\"+%2818+%2B+c%29%2F3+=+12+\"$
\n" ); document.write( "(1) $\"+18+%2B+c+=+36+\"$
\n" ); document.write( "(1) $\"+c+=+36+-+18+\"$
\n" ); document.write( "(1) $\"+c+=+18+\"$
\n" ); document.write( "The 3rd number is 18 \n" ); document.write( "

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