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Slove this

  1. Oct 1, 2008 #1
    sum of 1 n = 20/ r = 1
    r(r+1)
     
  2. jcsd
  3. Oct 1, 2008 #2

    mathman

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    It would help if you could clarify your expression.
     
  4. Oct 4, 2008 #3
    If construed as a number theory problem, the best that I could come up with

    sum of 1 to n = r(r+1) sum of 1 to 3 = 2*3 etc.
    sum of 1 to n = 20/r sum of 1 to 4 = 20/2
    So r = 2
     
    Last edited: Oct 4, 2008
  5. Oct 5, 2008 #4

    mathman

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    If I understand you correctly, you are summing the integers from 1 to n.
    This sum is n(n+1)/2. I have no idea what you mean by r.
     
  6. Oct 5, 2008 #5
    This topic made me laugh for some reason.
     
  7. Oct 5, 2008 #6
    I viewed it as two diophantine equations in two variables

    n(n+2)/2 = r(r+1) and m(m+1)/2 = 20/r for which the only solution is n = 3, m =4, r = 2

    I did not use the formula n(n+1)/2 since I knew the values of n(3) and n(4) already.

    No certainty that I understood the problem correctly though I don't see how there could be a different problem intended.
     
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