document.write( "Question 1116177: How many four digits number can be formed with the 10 digits 0-9
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Algebra.Com's Answer #731007 by ikleyn(52814) $\"\"$ $\"About$

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document.write( "a)  Answer.  9000 four digit numbers.\r\n" );
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document.write( "             It is the full number of existing 4-digit numbers, \r\n" );
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document.write( "             and it is how many four digits number can be formed with the 10 digits 0-9,  if repetitions are allowed.\r\n" );
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document.write( "b)  Answer.  9*9*8*7 = 4536.\r\n" );
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document.write( "              Very first (the left-most) digit can be any of 9 digits from 1 to 9\r\n" );
document.write( "                   (zero is excluded in this position);\r\n" );
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document.write( "              Next digit can be any of 9 remaining digits (zero is included in this position)\r\n" );
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document.write( "              Next digit can be any of 8 remaining digits;\r\n" );
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document.write( "              Next (and the last) digit can be any of 7 remaining digits.\r\n" );
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document.write( "              In all, there are  9*9*8*7 opportunities.\r\n" );
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document.write( "b)  Answer.  9*8*7 = 504.\r\n" );
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document.write( "              The digit zero is fixed in the \"ones\" position.\r\n" );
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document.write( "              Very first (the left-most) digit can be any of 9 digits from 1 to 9\r\n" );
document.write( "                   (zero is excluded in this position);\r\n" );
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document.write( "              Next digit can be any of 8 remaining digits;\r\n" );
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document.write( "              Next digit can be any of 7 remaining digits.\r\n" );
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document.write( "              In all, there are  9*8*7 opportunities.              \r\n" );
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