Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie
Hi there,
There is an issue with role permissions that is being worked on at the moment.
If you are having trouble with access or permissions on regional forums please post here to get access: https://www.boards.ie/discussion/2058365403/you-do-not-have-permission-for-that#latest

Probability question

  • 06-01-2014 9:48am
    #1
    carrick76
    Registered Users, Registered Users 2 Posts: 80 ✭✭


    I have a question on how to calculate the probability.

    If there is a 1 in 5 chance of something happening. E.g. if there are 5 marbles in a bag and one is a different colour.

    What is the probability if I pick a marble out 10 times (and replace it) that I get the differently coloured marble 5 times out of 10.

    Thanks


Comments

  • #2
    Yakuza
    Registered Users, Registered Users 2 Posts: 5,141 ✭✭✭Yakuza


    That's a question that requires the use of the binomial distribution, with a success probability of 20%. Does that help? have a bash at it now and post up your attempt.


  • #3
    carrick76
    Registered Users, Registered Users 2 Posts: 80 ✭✭carrick76


    Yakuza wrote: »
    That's a question that requires the use of the binomial distribution, with a success probability of 20%. Does that help? have a bash at it now and post up your attempt.


    Thanks, that helps a lot. Are you a teacher? :)

    A long time since I did such maths.:o

    Found an online binomial calculator and its telling me >/= 5/10 has a probability of 3.3%. Does that seem right?

    Seems about right to me but thought it would be slightly higher.

    Thanks again


  • #4
    Yakuza
    Registered Users, Registered Users 2 Posts: 5,141 ✭✭✭Yakuza


    Nope, not a teacher (formally anyway, though I do try to impart some maths and science to my kids). I work in the insurance/IT/Actuarial worlds so this maths is still reasonably fresh in my mind.

    Your answer looks a little high to me. Forget online calculators, go back to first principles...

    Define a success as getting the different-coloured ball out of the bag, this has a 1 in 5 chance of success and a 4 in 5 chance of failure.

    So, to get 5 successes from 10 trials, you must have 5 successes (with what probability? )and 5 failures (with what probability?), and these can happen in
    [latex]{10 \choose 5}[/latex] different ways. What do you get when you multiply all this out?

    Hint: use http://mathworld.wolfram.com/BinomialDistribution.html


Advertisement