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

Binomial distribution bias

  1. Oct 23, 2004 #1
    binomial distribution

    Prob of rolling a 1 = 1/10, rolling a 2 = 2/10, 3 = 3/10, 4 = 4/10
    Let X be the value thrown
    Calculate E(X) and Var(X)


    To do this can't use E(X) = np and can't use Var(X) = npq
    is this correct?
     
    Last edited: Oct 23, 2004
  2. jcsd
  3. Oct 23, 2004 #2

    matt grime

    User Avatar
    Science Advisor
    Homework Helper

    This isn't a binomial distribution, so no using those formulae won't help.
     
  4. Oct 23, 2004 #3

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    You can, however, use the basic definitions:

    E(x)= &Sigma(xProb(x))= 1*prob(1)+ 2*prob(2)+ 3*prob(3)+ 4*prob(4).

    &sigma(x)= &sqrt((x- E(x))2Prob(x)).
     
  5. Oct 23, 2004 #4
    thanks alot,

    so to use those formula, we could find that the E(X) amount of 4's, out of 10 rolls, would be

    4/10 * 10 = 4

    and the variance 4/10 * 6/10 * 10 = 2.4
     
    Last edited: Oct 23, 2004
  6. Oct 24, 2004 #5

    matt grime

    User Avatar
    Science Advisor
    Homework Helper

    "E(X) amount of 4's"

    E(X) is the expectation of the score. I don't see what the 'amount of 4s' has to do with it.

    As was written above the expectation is:

    1/10 + 2*2/10 + 3*3/10 +4*4/10 = 3.
     
  7. Oct 27, 2004 #6
    yes, i know
    i wanted to know a use of the E(X) = np formual with respect to that question, the use of it was to find the probability of the amount of 4's out of 10 rolls
     
  8. Oct 27, 2004 #7

    matt grime

    User Avatar
    Science Advisor
    Homework Helper

    In that case why did you use X for two different things? The outcome of one throw and the number of 4s occuring in 10 rolls?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Binomial distribution bias
  1. Binomial distribution (Replies: 3)

  2. Binomial Distribution (Replies: 1)

  3. Binomial distribution (Replies: 3)

  4. Binomial distribution (Replies: 1)

Loading...