No area code begin with 1 or 0.
So for the 1st digit you have 8 possibilities
10 possibilities for the 2nd and 3rd digits.
8 X 10 X 10 = 800 possibilities
RohnHow do I calculate the # of possible area codes?
Stage 1. 9 possibilities since "1" is taken out, therefore the restriction is "9 x.."
Stage 2. No restriction, repetitions are allowed, so 10 possibilities.
Stage 3. No restrictions, repetitions are allowed, so 10 possibilities .
By the Fundamental Counting Principle, 9 x 10 x 10 = 900
Therefore, there are 900 possible combination of area codes.
@Rohn: there is no restriction on the first digit not having a 0.How do I calculate the # of possible area codes?
You can get the full story (and more) about Area Codes in North America
at http://www.nanpa.com/area_codes/index.ht鈥?/a>
(The website of the North American Number Plan Association)
Here's some text from their front page:
The format of an area code is NXX, where N is any digit 2 through 9 and X is any digit 0 through 9. Initially, the middle digit of an area code had to be "0" or "1". When this restriction was removed in 1995, additional area code combinations became available. There are 800 possible combinations associated with the NXX format. Some of these combinations, however, are not available or have been reserved for special purposes
Among them are the following:
Easily Recognizable Codes When the second and third digits of an area code are the same, that code is called an easily recognizable code (ERC). ERCs designate special services; e.g., 888 for toll-free service.
N11 These 8 ERCs, called service codes, are not used as area codes.
N9X The 80 codes in this format, called expansion codes, have been reserved for use during the period when the current 10-digit NANP number format undergoes expansion.
37X and 96X Two blocks of 10 codes each have been set aside by the INC for unanticipated purposes where it may be important to have a full range of 10 contiguous codes available.
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