Until recently, telephone area codes in the United States, Canada, and the Caribbean islands were chosen according to the following rules: (i) The first digit cannot be 0 or a 1, and (ii) the second digit must be a 0 or a 1. But in 1995, the second rule was abandoned when the area code 360 was introduced in parts of western Washington State. Since then, many other new area codes that violate Rule (ii) have come into use, although Rule (i) still remains in effect.
(a) How many area code $+$ telephone number combinations were possible under the old rules? (See Exercise 6 for a description of local telephone numbers.)
(b) How many area code $+$ telephone number combinations are now possible under the new rules?
(c) Why do you think it was necessary to make this change?
(d) How many area codes that violate Rule (ii) are you personally familiar with?