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Math Help - Need Help.

  1. #1
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    Need Help.

    There are 24 four-digit numbers that can be formed by permuting 3, 5, 7, and 9. What is the sum of all these numbers?
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  2. #2
    MHF Contributor
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    Re: Need Help.

    Quote Originally Posted by ConnieLam View Post
    There are 24 four-digit numbers that can be formed by permuting 3, 5, 7, and 9. What is the sum of all these numbers?
    I don't know how much this will help but here's your answer. I just brute forced it. There's probably a more elegant way.

    Need Help.-clipboard01.jpg

    Ok, here's a more elegant way.

    Each digit will appear in each 10's place 6 times. Thus the total is

    $6\times (3+5+7+9)(1000+100+10+1) = 159984$
    Last edited by romsek; April 18th 2014 at 04:50 PM.
    Thanks from ConnieLam
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  3. #3
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    Re: Need Help.

    Thanks. You helped a lot.
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