What’s the probability? Open your local telephone directory to any page in the residential listing. Look at the last four digits of each telephone number, the digits that specify an individual number within an exchange given by the first three digits. Note the first of these four digits in each of the first 100 telephone numbers on the page.

(a) How many of the digits were 1, 2, or 3? What is the approximate probability that the first of the four “individual digits” in a telephone number is 1, 2, or 3?

(Hint: See pages 377–378.)

(b) If all 10 possible digits had the same probability, what would be the probability of getting a 1, 2, or 3? Based on your work in (a), do you think the first of the four “individual digits” in telephone numbers is equally likely to be any of the 10 possible digits? (Hint: See pages 377 and 397–399.)