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.
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.
7891244 or 4421987 or 5768937 or 9078564 and lastly 5658664
8,000,000 million telephone numbers are possible with these conditions, corresponding to the numbers 2,000,000 - 9,999,999. Many countries have forced dialing of the area code now, creating telephone numbers with a minimum of 10 digits. This means there are 8 million possible telephone numbers in each area code. (area code of 3 digits long).
5 digit telephone numbers having at least one of their digits repeated is = total possible 5 digit telephone numbers - 5 digit telephone numbers without any digit being repeated. =(10*10*10*10*10)-(10*9*8*7*6) =100000-30240 =69760
7
763920
That makes:* 8 options for the first digit * 8 options for second digit * 10 options for the third digit * ... etc. Just multiply all the numbers together.
because they didnt know the other digits.
10,000
Telephone numbers in Turkey consist of the telephone country code +90, followed by a three-digit area code and a 7-digit subscriber number.
Telephone numbers throughout Russia are uniformly 3 digits for the area code plus 7 digits for the local number.
Assuming that the first digit of the 4 digit number cannot be 0, then there are 9 possible digits for the first of the four. Also assuming that each digit does not need to be unique, then the next three digits of the four can have 10 possible for each. That results in 9x10x10x10 = 9000 possible 4 digit numbers. If, however, you can not use the same number twice in completing the 4 digit number, and the first digit cannot be 0, then the result is 9x9x8x7 = 4536 possible 4 digit numbers. If the 4 digit number can start with 0, then there are 10,000 possible 4 digit numbers. If the 4 digit number can start with 0, and you cannot use any number twice, then the result is 10x9x8x7 = 5040 possilbe 4 digit numbers.
A telephone number in Lesotho are eight digits long with the first two numbers being its area code.
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