document.write( "Question 662008: Compute the number of four-digits integers whose digits are all odd or all even. \n" ); document.write( "
Algebra.Com's Answer #411906 by Edwin McCravy(20060)\"\" \"About 
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Compute the number of four-digits integers whose digits are all odd or all even.
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document.write( "First we compute the number of four-digit numbers whose \r\n" );
document.write( "digits are all odd\r\n" );
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document.write( "There are 5 odd digits, 1,3,5,7,9.\r\n" );
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document.write( "We can choose the first odd digit 5 ways.\r\n" );
document.write( "We can choose the second odd digit 5 ways.\r\n" );
document.write( "We can choose the third odd digit 5 ways.\r\n" );
document.write( "We can choose the fourth odd digit 5 ways.\r\n" );
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document.write( "That's 5·5·5·5 = 54 = 625 ways\r\n" );
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document.write( "Next we compute the number of four-digit numbers whose \r\n" );
document.write( "digits are all even\r\n" );
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document.write( "There are 5 even digits, 0,2,4,6,8. The difference \r\n" );
document.write( "between this and above is that 0 cannot be the first digit \r\n" );
document.write( "of a 4 digit number.\r\n" );
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document.write( "We can choose the first even digit only 4 ways, \r\n" );
document.write( "since it cannot be 0.\r\n" );
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document.write( "We can choose the second even digit 5 ways.\r\n" );
document.write( "We can choose the third even digit 5 ways.\r\n" );
document.write( "We can choose the fourth even digit 5 ways.\r\n" );
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document.write( "That's 4·5·5·5 = 4·53 = 500 ways.\r\n" );
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document.write( "So that's a total of 625+500 = 1125.\r\n" );
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document.write( "Edwin
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