In order to test a vaccine, we have to find patients with a certain blood type, that is found in 20% of the population. Model W, the number of people sampled until we have found one with thhis blood type; X, the number sampled to find four with the blood type; and Y, the number with this blood type among 20 people. Find the means and standard deviations of W, X and Y.
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A mean and standard deviation are found. A recurrence relation is investigated. The solution is detailed and well presented. The response received a rating of "5" from the student who originally posted the question.