Canadian Blood Services tests blood donations for West Nile Virus according to the following protocol. Samples from units of blood are pooled, six units at a time, and the pool of six is tested for the presence of West Nile Virus. If any unit comes from a donor with West Nile Virus, the pool tests positive.

a) A blood drive is being held in a particular town. Suppose the actual prevalence of West Nile Virus in the town is 1 in 500. Assuming independence between donors, find the probability that a randomly selected pool of six units test positive.

b) A blood drive is held in the town and 216 people donate. Find the probability that at least one pool of 6 units tests positive from the blood drive.

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