document.write( "Question 1036831: 20Cr = 20C(r+2), find the value of r.
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Algebra.Com's Answer #651547 by Edwin McCravy(20060)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "For all positive integers n and r, where n ≥ r ≥ 0\r\n" );
document.write( "nCk = nC(n-k)\r\n" );
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document.write( "If you mean 20Cr = 20C(r+2), then since r+2 > r, we turn nCk = nC(n-k)\r\n" );
document.write( "around as\r\n" );
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document.write( " nC(n-k) =  nCk\r\n" );
document.write( "20Cr     = 20C(r+2)\r\n" );
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document.write( "n=20, r=n-k, k=r+2\r\n" );
document.write( "      r=20-k\r\n" );
document.write( "      r=20-(r+2)\r\n" );
document.write( "      r=20-r-2\r\n" );
document.write( "      r=18-r\r\n" );
document.write( "     2r=18\r\n" );
document.write( "      r=9\r\n" );
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document.write( "Checking\r\n" );
document.write( "  20Cr = 20C(r+2)\r\n" );
document.write( "  20C9 = 20C(9+2)\r\n" );
document.write( "  20C9 = 20C11\r\n" );
document.write( "167960 = 167960\r\n" );
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document.write( "Edwin

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