According to the Centers for Disease Control and Prevention (CDC), the aging of the U.S. population is translating into many more visits to doctors’ offices and hospitals. It is estimated that an average person makes four visits a year to doctors’ offices and hospitals. 

a. What are the mean and the standard deviation of an average person’s number of monthly visits to doctors’ offices and hospitals? 

b. What is the probability that an average person does not make any monthly visits to doctors’ offices and hospitals? 

c. What is the probability that an average person makes at least one monthly visit to doctors’ offices and hospitals?