document.write( "Question 1189187: How many positive 3-digit integers have a units (ones) digit of 9? \n" ); document.write( "

Algebra.Com's Answer #820472 by ikleyn(52777) $\"\"$ $\"About$

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document.write( "First (left-most) digit can be any from 1 to 9.\r\n" );
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document.write( "Next (tens) digit can be any from 0 to 9.\r\n" );
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document.write( "Therefore, there are 9*10 = 90 such three-digit numbers.\r\n" );
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\n" ); document.write( "\n" ); document.write( "Even more simple reasoning is possible.\r
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document.write( "Consider the set of all such 3-digit numbers. \r\n" );
document.write( "Cut the last digit: you will get the set of all 2-digit numbers.\r\n" );
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document.write( "The cardinality of this set of 2-digit numbers is 90 - - - it gives the answer.\r\n" );
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