Results 1 to 3 of 3

Math Help - ahh help please (normal approx. to binomial distribution)

  1. #1
    Newbie
    Joined
    Oct 2008
    Posts
    11

    ahh help please (normal approx. to binomial distribution)

    The human resources manager at a company knows that 34% of the workforce belong to a union. If she randomly surveys 50 employees, what is the probability that exactly 30 of them do not belong to a union?


    p=0.34 q=0.66 n=50 np=17

    p(x<30)=p(x<29)=p(x<29.5)


    6=((square root)(npq))
    =3.33

    z1=x1 - x /6
    =29.5-17/3.33
    =3.73?????????
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Oct 2008
    Posts
    11
    do I need to subtract 3.73 by one?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Senior Member
    Joined
    Dec 2007
    From
    Melbourne
    Posts
    428
    p=0.34 q=0.66 n=50 np=17

    p(x<30)=p(x<29)=p(x<29.5)


    6=((square root)(npq))
    =3.33

    z1=x1 - x /6
    =29.5-17/3.33
    =3.73?????????
    What you have established with this working is that P(X<30) = P(Z<3.73) where Z has the standard normal distribution. When you use this approximation, it is assumed that you have a table to look up P(Z<3.73) in, so feel free to get a probability from your calculator, then find P(X>30) in the same way.

    I would like to point out though that this question is much easier done exactly: P(X=x) = {n \choose x} p^xq^{n-x}. I never liked the normal approximation, it never seemed logical to me that I should approximate something calculable by hand with something that isn't.

    also
    p(x<30)=p(x<29)=p(x<29.5)
    should read  P(X<30 = P(X\leq29) = P(X<29.5), but I suspect this was just an issue with typing the symbols
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Normal approximation to binomial distribution.
    Posted in the Statistics Forum
    Replies: 9
    Last Post: June 22nd 2010, 08:36 AM
  2. combining binomial & normal distribution
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: May 14th 2010, 08:42 PM
  3. Normal approximation to the binomial distribution
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: March 16th 2010, 03:59 PM
  4. Normal approx to the binomial dist. questions
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: February 1st 2010, 06:44 PM
  5. Proving binomial to approx normal by CLT
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: November 16th 2008, 12:11 PM

Search Tags


/mathhelpforum @mathhelpforum