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Nov 2013 p62 q5
3041
On trains in the morning rush hour, each person is either a student with probability 0.36, or an office worker with probability 0.22, or a shop assistant with probability 0.29 or none of these.
8 people on a morning rush hour train are chosen at random. Find the probability that between 4 and 6 inclusive are office workers.
Solution
The problem involves a binomial distribution where the probability of being an office worker is given as 0.22. The probability of not being an office worker is therefore 1 - 0.22 = 0.78.
We need to find the probability that between 4 and 6 people inclusive are office workers out of 8 people. This is calculated using the binomial probability formula:
\(P(X = r) = \binom{n}{r} p^r (1-p)^{n-r}\)
where \(n = 8\), \(p = 0.22\), and \(r\) is the number of office workers.