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Simple number game

  1. Aug 12, 2004 #1
    What 4 digit number is equal to two more than twice the reverse of its digits?
    Do it without without using a computer or writing it down. All in your head.
  2. jcsd
  3. Aug 13, 2004 #2
    So nobody can do this? Its pretty easy to think about. Since it stays a 4 digit number, that means that the 1's digit of the number must be 4 or less, because once its reversed and doubled, it would be over 10, which would make it a 5 digit number.
    Then you can think, well, since the 1000ths digit must be doubled then add two, and equal a number 4 or less(once its reversed), it can be : 0,1,5,6.

    You can also do this by computer to check you answer, which is a most unfun way of doing it. a*1000+b*100+c*10+d*1 = d*2000+c*200+b*20+d*2+2
  4. Aug 13, 2004 #3


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    I can't do it in my head :grumpy: Surely one of the other digits will have to be greater than 4...and that involves carry-overs and related difficulties. Will need paper ! :cry:
  5. Aug 13, 2004 #4


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    Surely you mean:
    a*1000+b*100+c*10+d*1 = d*2000+c*200+b*20+a*2+2

    The answer is 5992.
  6. Aug 13, 2004 #5
    5992, of course :-)
  7. Aug 13, 2004 #6


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    Yeah, I used Excel. <cheater>
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