Answer:
Each three-digit area code may contain up to 7,919,900 unique phone numbers:
NXX may begin only with the digits [2–9], providing a base of 8 million numbers: ( 8 x 100 x 10000 ) .
However, the last two digits of NXX cannot both be 1, to avoid confusion with the N11 codes (subtract 80,000).
Despite the widespread usage of NXX "555" for fictional telephone numbers — see 555 (telephone number) — today, the only such numbers specifically reserved for fictional use are "555-0100" through "555-0199", with the remaining "555" numbers released for actual assignment as information numbers (subtract 100).
In individual geographic area codes, several other NXX prefixes are generally not assigned: the home area code(s), adjacent domestic area codes and overlays, area codes reserved for future relief nearby, industry testing codes (generally NXX 958 and 959) and special service codes (such as NXX 950 and 976). Subtract for 911 411etc emergency and informational numbers
Step-by-step explanation:
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There are total 8 X 10⁹ possible 10 digit phone numbers whose first digit cannot be 0 and 1.
A permutation of a set is, loosely speaking, an arrangement of its members into a sequence or linear order, or if the set is already ordered, a rearrangement of its elements.
Here, well the first digit is not allowed to be 0 or 1 so 8 (2 to 9) remain to choose.
For the reminding 8 numbers you can make any choice from 00000000 to 99999999 when you count them these are 10⁹ possibilities and when you consider the 8 possibilities you have for the first number there are 8X10⁹ possibilities total.
Thus, there are total 8 X 10⁹ possible 10 digit phone numbers whose first digit cannot be 0 and 1.
Learn more about Permutation from:
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