On average, 20 households in 50 own answering machines.
a. Using the Poisson formula, find the probability that in a random sample of 50 households, exactly 25 will own answering machines.
b. Using the Poisson probabilities table, find the probability that the number of households in 50 who own answering machines is
i. At most 12
ii. 13 to 17
iii. At least 30