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Math Help - Simple Probability Problem

  1. #1
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    Simple Probability Problem

    I have a simple probability problem I can't get for the life of me must be over thinking it.

    It is said that 40% of students drink coffee in the morning before class. If a group of 25 students were polled, what is the probability of 15 of them drinking coffee?

    Any help would be appreciated thanks
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  2. #2
    MHF Contributor harish21's Avatar
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    Quote Originally Posted by action259 View Post
    I have a simple probability problem I can't get for the life of me must be over thinking it.

    It is said that 40% of students drink coffee in the morning before class. If a group of 25 students were polled, what is the probability of 15 of them drinking coffee?

    Any help would be appreciated thanks
    I think this involves Binomial distribution. have you ever heard of it?
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  3. #3
    Super Member Anonymous1's Avatar
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    Quote Originally Posted by action259 View Post
    I have a simple probability problem I can't get for the life of me must be over thinking it.

    It is said that 40% of students drink coffee in the morning before class. If a group of 25 students were polled, what is the probability of 15 of them drinking coffee?

    Any help would be appreciated thanks
    P(drinks coffee)= 40% = 2/5 right...

    We have n= 25 students in total...

    Define a success as "A student drinks coffee."

    Then,

    number of students that drink coffee = \{ the number successes with P(success)= 2/5\} ~ Binomial(n=25,p=2/5).

    Also, we know the probability mass function is:

    P(X=k)= {n\choose k}(p)^n (1-p)^{n-k}. Therefore,

    P(X=15)= {25\choose 15}(2/5)^{25} (1-2/5)^{25-15}. Now throw that in your calculator.
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  4. #4
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    Ok that makes sense Thanks
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