Question

A.US phone numbers traditionally do not start with a zero or a one, otherwise there are no other restrictions, so how many 7 digit phone numbers are possible?

B.Some cities have now required you to dial area codes first. For example in Chicago we either dial 773 or 312, so now how many possible Chicago Phone numbers are there?

C.Why have cities and suburbs have added on these area codes in recent years?

Answer 1

Number of ways of choosing the first digit = 8 ways
Number of ways of choosing the rest of the digits = 10^6
Therefore, 8 x 10^6 7-digit phone numbers are possible.