Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: The Sum Of Σ

  1. Oct 22, 2005 #1
    The Sum Of....Σ

    So we were given this awkward question to do out of the text book... and a classmate and I arrived at similiar answers.... for part of the question, we are supposed to right a sequence into "sum notation"

    Could somebody please tell me if my notation is correct?

    Say... we have a binomial random variable... X ~ binomial (n, p)

    P(X ≥ k) = P(X=k) + P(X = k +1) + ...... + P(X = n)
    = (nCk)(p^k)(1-p)^n-k + (nCk+1)(p^k+1)(1-p)^n-(k+1)
    = "the sum of i = k to the n" (nCi)(p^i)(1-p)^n-1

    I know its messy... but "the sum of i = k to the n" (nCi)(p^i)(1-p)^n-1

    but im looking to see if thats right?

    Thanks
     
  2. jcsd
  3. Oct 22, 2005 #2
    oh and by the way... that (nCk) or (nCi) means "N choose k" or "N choose i"
     
  4. Oct 22, 2005 #3

    HallsofIvy

    User Avatar
    Science Advisor

    [tex]\Sigma_{i= k}^n _nC_i p^i(1- p)^{n-i}[/tex]

    NOT "i= k to the n", that would be i= kn!

    And it is (1-p)n-i, not (1-p)n-1.
     
  5. Oct 22, 2005 #4
    oh... how do you make your equations look so nice? I belive that its some softwear that you use?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook