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Homework Help: Caculate the probability using a binomial distribution

  1. Jun 3, 2007 #1
    Ok so I have a problem I am not sure of the method I should use. In a recent survey, 60% of the population disagreed with a given statement, 20% agreed and 20% were unsure. Find the probability of having at least 5 person who agree in a mini-survey with 10 people.

    I tried to caculate the probability using a binomial distribution with n=10, p=0,2 agree and 1-p = 0,8 who either agree or are unsure, and

    P(X) = (n!/ (k!(n-k)!)) (p^x) ((1-p) ^(n-x))

    I added p(5), p(6)... p(10) and I got p(total) = 0,0328

    Is it right to use a binomial distribution in this case?
  2. jcsd
  3. Jun 3, 2007 #2


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    Yes, that is the correct distribution to use.
  4. Jun 3, 2007 #3


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    Yes. The number of people agreeing with the statement in n trials is random variable with a binomial probability distribution. This is because each individual event or trial has two possible outcomes (agreement or not agreement, if you choose to group them that way), and as a result is described by a Bernoulli random variable.
  5. Jun 4, 2007 #4
    Thank you!
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