document.write( "Question 160888: A social security number consists of nine digits. How many different Social Security numbers are possible if repetition is permitted? \n" ); document.write( "
Algebra.Com's Answer #118591 by Edwin McCravy(20056)\"\" \"About 
You can put this solution on YOUR website!
A social security number consists of nine digits. How many different Social Security numbers are possible if repetition is permitted?
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document.write( "First way:\r\n" );
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document.write( "Obviously there are 999999999 social security numbers in this list:\r\n" );
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document.write( "000-00-0001\r\n" );
document.write( "000-00-0002\r\n" );
document.write( "...........\r\n" );
document.write( "...........\r\n" );
document.write( "...........\r\n" );
document.write( "999-99-9997\r\n" );
document.write( "999-99-9998\r\n" );
document.write( "999-99-9999\r\n" );
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document.write( "For that's the same as counting for 1 to 999999999.\r\n" );
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document.write( "But there is one more not in the list, namely 000-00-0000.\r\n" );
document.write( "So there are 1000000000 or 1 billion social security numbers.\r\n" );
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document.write( "A second way to do it is this way:\r\n" );
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document.write( "Suppose a social security number is \r\n" );
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document.write( "ABC-DE-FGHI\r\n" );
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document.write( "There are 10 choices for a digit to go in the A position\r\n" );
document.write( "There are 10 choices for a digit to go in the B position\r\n" );
document.write( "There are 10 choices for a digit to go in the C position\r\n" );
document.write( "There are 10 choices for a digit to go in the D position\r\n" );
document.write( "There are 10 choices for a digit to go in the E position\r\n" );
document.write( "There are 10 choices for a digit to go in the F position\r\n" );
document.write( "There are 10 choices for a digit to go in the G position\r\n" );
document.write( "There are 10 choices for a digit to go in the H position\r\n" );
document.write( "There are 10 choices for a digit to go in the I position\r\n" );
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document.write( "So that's 10*10*10*10*10*10*10*10*10 = 1000000000.\r\n" );
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document.write( "Edwin
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