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How many numbers greater than 600 can be formed from the digits 2,3,4,6 if
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\r\n" ); document.write( "The first digit can only be 6\r\n" ); document.write( "
\n" ); document.write( "a. No digit is used twice
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document.write( "Three-digit numbers:\r\n" );
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document.write( "Choose the 1st digit 1 way, as 6.\r\n" );
document.write( "Choose the 2nd digit as any of the 3 remaining digits {2,3,4}.\r\n" );
document.write( "Choose the 3rd digit as any of the 2 remaining digits. \r\n" );
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document.write( "That's 1*3*2 = 6 three digit numbers. We can just list them:\r\n" );
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document.write( "1. 623\r\n" );
document.write( "2. 624\r\n" );
document.write( "3. 632\r\n" );
document.write( "4. 634\r\n" );
document.write( "5. 642\r\n" );
document.write( "6. 643 \r\n" );
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document.write( "Four-digit numbers:\r\n" );
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document.write( "That's also 6 because in each of the cases above we just put \r\n" );
document.write( "the 1 remaining digit on the end of each of those 6 three-digit\r\n" );
document.write( "numbers above.\r\n" );
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document.write( "1. 6234\r\n" );
document.write( "2. 6243\r\n" );
document.write( "3. 6324\r\n" );
document.write( "4. 6342\r\n" );
document.write( "5. 6423\r\n" );
document.write( "6. 6432 \r\n" );
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document.write( "Total: 6+6 = 12.\r\n" );
document.write( "\n" ); document.write( "b. No such rule exists
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\r\n" ); document.write( "Infinitely many because 666666666666666666666666666666\r\n" ); document.write( "is possible or even numbers that stretch out to the moon. :)\r\n" ); document.write( "\r\n" ); document.write( "Edwin\n" ); document.write( "