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Nov 2012 p61 q6
3323
Ana meets her friends once every day. For each day the probability that she is early is 0.05 and the probability that she is late is 0.75. Otherwise she is on time.
Find the probability that she is on time on fewer than 20 of the next 96 days.
Solution
The probability that Ana is on time on any given day is:
\(p = 1 - 0.05 - 0.75 = 0.2\)
We are looking for the probability that she is on time on fewer than 20 out of 96 days. This is a binomial distribution problem with parameters \(n = 96\) and \(p = 0.2\).
We approximate the binomial distribution with a normal distribution: