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Thread: "Use the normal approximation to the binomial distribution" help if possible?

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    "Use the normal approximation to the binomial distribution" help if possible?




    Hello, i'm new here and i'm stuck on a question.

    This isn't really from my homework, as i'm just reviewing for my final which is in a week.

    The question is:

    "It is estimated that 20% of teenagers smoke atleast 10 cigarettes daily. Use the normal approximation to the binomial distribution to determine the probability that between 45 and 55 teenagers from 200 randomly chosen teenagers smoke atleast 10 cigarettes daily."


    I take it that:

    n = 200
    p = .2
    q = .8

    np = 40
    and the square root of npq = 5.6568

    My problem is that i don't really understand where to go from here, i mean, i remember something about using normalcdf(___,____, mean, standard deviation) = probability



    However, when I do this, it doesn't give me the answer that's in my multiple choice question.

    a) 0.161
    b) 0.184
    c) 0.207
    d) 0.210

    The answer is b

    Am I supposed to do something else? Like, look at this question differently or what? This is for my math 12 course in Highschool, and we did it in the beginning of the semester so I'm panicking because I dont remember what to do.

    Thank you.
    Last edited by uns33n; 01-07-2007 at 01:08 AM.

  2. #2
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    Quote Originally Posted by uns33n View Post
    Hello, i'm new here and i'm stuck on a question.

    This isn't really from my homework, as i'm just reviewing for my final which is in a week.

    The question is:

    "It is estimated that 20% of teenagers smoke atleast 10 cigarettes daily. Use the normal approximation to the binomial distribution to determine the probability that between 45 and 55 teenagers from 200 randomly chosen teenagers smoke atleast 10 cigarettes daily."


    I take it that:

    n = 200
    p = .2
    q = .8

    np = 40
    and the square root of npq = 5.6568

    My problem is that i don't really understand where to go from here, i mean, i remember something about using normalcdf(___,____, mean, standard deviation) = probability



    However, when I do this, it doesn't give me the answer that's in my multiple choice question.

    a) 0.161
    b) 0.184
    c) 0.207
    d) 0.210

    The answer is b

    Am I supposed to do something else? Like, look at this question differently or what? This is for my math 12 course in Highschool, and we did it in the beginning of the semester so I'm panicking because I dont remember what to do.

    Thank you.
    Okay sorry, I have figured it out, I couldn't find a delete thread button. I apologize.


    what I had to do was:

    normalcdf(45,55,40, 5.6568) = .184

    I apologize, i was panicking.

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