document.write( "Question 1143953: How many two-digit odd numbers can you form using the digits 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9? Repetitions are not allowed. \n" ); document.write( "

Algebra.Com's Answer #764908 by ikleyn(52781) $\"\"$ $\"About$

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document.write( "The \"ones\" digit must be  \"1\", or \"3\",  or\"5\",  or \"7\",  or \"9\" -- in all, 5 options.\r\n" );
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document.write( "The \"tens\" digit then can be any of 8 remaining digits (\"0\" is excluded as the leading digit).\r\n" );
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document.write( "Therefore, 5*8 = 40 two-digit numbers are possible, satisfying given conditions.\r\n" );
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document.write( "In all, there are 90 two-digit numbers, from 10 to 99.\r\n" );
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document.write( "Of them, one half, i.e. 45 numbers, are even and the other half, i.e. 45 numbers, are odd.\r\n" );
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document.write( "Of 45 odd numbers, exclude these five numbers  11, 33,  55,  77  and  99, since they have two repeating digits.\r\n" );
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document.write( "The rest 40 = 45 - 5 two-digit numbers satisfy the problem's conditions.\r\n" );
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