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 1

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.

Answer 2

It depends entirely on the local number length.

In the UK, local numbers cannot begin with a 0 or a 1.

They also cannot begin with 999, as dialling that number calls the emergency services.

Usually all local numbers beginning 990 to 999 aren't issued either.

This gives, for:

4-digit numbers - 7 900

5-digit numbers - 79 000

6-digit numbers - 790 000

7-digit numbers - 7 900 000

8-digit numbers - 79 000 000

Since most UK numbers have 10 digits, this means the valid formats are:

5+5

4+6

3+7

2+8

For the small number of places with 9 digit numbers, the valid formats are:

5+4

4+5

For "A+N", the "A" describes how many digits are in the Area code, and the "N" describes how many digits are in the local Number part.

The '0' trunk code is not counted as being a part of the area code.

Answer 3

7891244 or 4421987 or 5768937 or 9078564 and lastly 5658664