The number of tubes of toothpaste purchased by a typical family is a random variable having a Poisson distribution with an average of 1.8 tubes per month.
(a) What is the probability that a typical family will purchase at least three tubes of toothpaste in any given month?
(b) What is the likelihood that a typical family will purchase less than four tubes of toothpaste in any given month?
Note: Calculate all the probabilities using the Poisson formula and then the Excel function POISSON.