document.write( "Question 479742: ncr=220 and npr=1320 find n and r \n" ); document.write( "

Algebra.Com's Answer #328692 by edjones(8007) $\"\"$ $\"About$

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nCr=n!/((n-r)!r!), nPr=n!/(n-r)!
\n" ); document.write( "nCr=nPr/r!
\n" ); document.write( "nCr*r!=nPr
\n" ); document.write( "220*r!=1320
\n" ); document.write( "r!=6
\n" ); document.write( "r=3
\n" ); document.write( "nP3=n!/(n-3)!=1320
\n" ); document.write( "n*(n-1)*(n-2)=1320
\n" ); document.write( "n^3-3n^2+2n=1320
\n" ); document.write( "n^3-3n^2+2n-1320=0
\n" ); document.write( "n=12
\n" ); document.write( ".
\n" ); document.write( "Ed \n" ); document.write( "

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