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

Question regarding binomial random variable and distribution

  1. Sep 15, 2009 #1

    just started learning probability & need some help in understanding....

    "The binomial random variable X associated with a binomial experiment consisting of n trials is defined as

    X = the number of S's among the n trials.

    Suppose, for example, that n = 3. Then there are 8 possible outcomes for the experiment:


    Why is it that there will be 8 possible outcomes?
  2. jcsd
  3. Sep 15, 2009 #2
    You have three trials--each trial has two possible results: S or F. Computing the total number of outcomes of the three trials is a matter of just adding together all of the separate results.

    First trial: 2 results, Second trial: 2 results, Third trial: 2 results

    2*2*2 = 23 = 8 outcomes

    The general formula is: Number of outcomes = pn, where p is the number of possible results of each trial, and n is the number of trials.

    If order doesn't matter, then in your example SSF and FSS would be considered the same outcome since the same number of S and F occur in both. The formula for this is different. Here's a link for more, I'm late for class...

  4. Sep 16, 2009 #3
    Thanks very much for the explaination. I understand why there 8 possible outcomes now. thanks again!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook