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Simple riddle

  1. Mar 20, 2003 #1
    Hi, I'm the guy formerly known as carsten. This is just a test to see if everything works.
    OK, you have the numbers
    1 2 3 4 5 6 7 8 9 0.
    You may insert some + signs and one = sign so to make a valid equation.
    Like
    12+34+5+6+78=90 (oops, false! )

    Happy posting, and a big thanks to Greg who does a great job IMO.
     
  2. jcsd
  3. Mar 20, 2003 #2
    Easy ..
    1+2+3+4+5+67+8=90 :smile:
     
  4. Mar 21, 2003 #3
    Yes. There's more solutions. :wink:
     
  5. Mar 21, 2003 #4

    drag

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    1 + 2 + 3 + 4 + 56 + 7 + 8 + 9 = 90
    12 + 3 + 45 + 6 + 7 + 8 + 9 = 90
     
  6. Mar 21, 2003 #5

    Njorl

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    You used the 9's twice drag.

    12+3+4+56+7+8=90
    1+23+45+6+7+8=90
    nothing =890
    nothing=7890
    etc.

    Njorl
     
  7. Mar 21, 2003 #6

    Njorl

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    If 2n-1 is prime, what can you say about (2n-1)*(2n-1)?

    Njorl
     
  8. Mar 21, 2003 #7
    Perfect!
     
  9. Mar 21, 2003 #8

    Njorl

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    Absolutely. I thought that would take longer.

    Njorl
     
  10. Mar 23, 2003 #9
    What do you mean perfect?
     
  11. Mar 24, 2003 #10

    Njorl

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    A perfect number is equal to the sum of its factors. For this purpose, 1 is considered a factor, but the number itself is not.

    Factors of 6 are 1,2,3 1+2+3=6
    Factors of 28 are 1,2,4,7,14 1+2+4+7+14=28

    6 and 28 are perfect.

    Njorl
     
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