Telephone numbers are made up of 7 digits but the first digit cannot be a 0 or 1 how many phone numbers are possible in each area code?

Answer is 9 million telephone numbers: from 100-0000 to 999-9999.

A 7-digit phone number is no different than a 7-digit number. Each digit can be unique. A 7-digit number can have 10 million combinations (from 0000000 to 9999999).

The problem says to exclude all phone numbers starting with a zero (as the first digit). This leaves out 1 million numbers (from 000-0000 to 099-9999).

Note: This does not look at what the phone companies consider to be valid or invalid phone numbers - since that wasn't in the question.