Results 1 to 6 of 6

Math Help - Binomial Distribution/Probability

  1. #1
    Newbie
    Joined
    Nov 2011
    Posts
    2

    Question Binomial Distribution/Probability

    Hi all,

    I'm having trouble with figuring out how to solve problems similar to the one below:

    Suppose the proportion of marbles that we get is as follows: 2 red, 2 green, 1 yellow and 1 blue. What is the probability that we'll get 3 red marbles out of 5?

    To get the probability, I tried to find the binomial probability:

    n = 5, r = 3, p = 0.4, q = 0.6

    5!/3!2! x 0.4^3 x 0.6^2 = 0.2304

    I'm told though that .2304 is not the right answer but I'm not sure why this is.

    Can anyone guide me to the right direction (is it really incorrect?)?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Mar 2008
    Posts
    934
    Thanks
    33
    Awards
    1

    Re: Binomial Distribution/Probability

    Quote Originally Posted by tardis View Post
    Hi all,

    I'm having trouble with figuring out how to solve problems similar to the one below:

    Suppose the proportion of marbles that we get is as follows: 2 red, 2 green, 1 yellow and 1 blue. What is the probability that we'll get 3 red marbles out of 5?

    To get the probability, I tried to find the binomial probability:

    n = 5, r = 3, p = 0.4, q = 0.6

    5!/3!2! x 0.4^3 x 0.6^2 = 0.2304

    I'm told though that .2304 is not the right answer but I'm not sure why this is.

    Can anyone guide me to the right direction (is it really incorrect?)?
    Where did you get p = 0.4?

    2/6 of the marbles are red, so...
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Nov 2011
    Posts
    53
    Thanks
    1

    Re: Binomial Distribution/Probability

    Ignore this. Totally wrong
    Last edited by takatok; November 14th 2011 at 05:50 PM.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Nov 2011
    Posts
    2

    Re: Binomial Distribution/Probability

    Ah... I think I've been staring at the problem for too long without realizing my mistake. Thank you!
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,738
    Thanks
    644

    Re: Binomial Distribution/Probability

    Hello, tardis!

    Very clumsy wording . . .


    There is a bag with 2 red, 2 green, 1 yellow and 1 blue marble.
    We draw 5 marbles with replacement.
    What is the probability that we will get 3 red marbles?

    The bag contains: 2 Reds and 4 Others.

    So we have: . \begin{Bmatrix}P(\text{Red}) &=& \frac{2}{6} &=& \frac{1}{3} \\ \\[-4mm] P(\text{Other}) &=& \frac{4}{6} &=& \frac{2}{3} \end{Bmatrix}

    P(\text{3 Red, 2 Others}) \;=\;{5\choose3}\left(\frac{1}{3}\right)^3\left( \frac{2}{3}\right)^2 \;=\;10\cdot\frac{1}{27}\cdot\frac{4}{9} \;=\;\frac{40}{243}

    Follow Math Help Forum on Facebook and Google+

  6. #6
    Junior Member
    Joined
    Nov 2011
    Posts
    53
    Thanks
    1

    Re: Binomial Distribution/Probability

    Agh! So sorry. I glanced too quickly at the problem and should have seen you were using 2 out of 5 instead of 2 out of 6 Even though its already correctly answered here is the correct table for completeness sake:

    Total Tries: 7776
    0: 1024 0.131687
    1: 2560 0.329218
    2: 2560 0.329218
    3: 1280 0.164609 <--- Your answer
    4: 320 0.0411523
    5: 32 0.00411523
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Probability for binomial distribution
    Posted in the Advanced Statistics Forum
    Replies: 4
    Last Post: March 7th 2012, 02:53 PM
  2. Probability and binomial distribution?
    Posted in the Statistics Forum
    Replies: 5
    Last Post: January 7th 2010, 06:11 AM
  3. Probability using binomial distribution
    Posted in the Statistics Forum
    Replies: 1
    Last Post: November 2nd 2009, 11:31 AM
  4. Binomial Probability Distribution on TI-89?
    Posted in the Calculators Forum
    Replies: 4
    Last Post: October 13th 2009, 04:36 AM
  5. Probability (Binomial distribution)
    Posted in the Statistics Forum
    Replies: 1
    Last Post: June 15th 2009, 11:16 PM

Search Tags


/mathhelpforum @mathhelpforum