How many unique phone numbers are there?
Each three-digit area code has a capacity of 7,919,900 telephone numbers: NXX may begin only with the digits [2–9], providing a base of eight million numbers: (8 × 100 × 10000). To avoid confusion with the N11 codes, the last two digits of NXX cannot both be 1.
How many combinations of 10 numbers are there?
How many combinations of 3 numbers are there?
Can we run out of phone numbers?
With ten digits, assuming a non-zero first digit, you can have 9,phone numbers.  estimates that the US population will hit a billion in 2100, so a few years from then is probably when we will run out of phone numbers. I don’t think end users will ever face a problem due to phone numbers running out.
Why is 555 a fake number?
Narrator: The short answer is that most 555 numbers are not working numbers, so real people won’t be harassed if diehard fans try to call them. 555 was an exchange combination that was not used very often in the American telephone system. You may get a wrong number, or no number at all.
Will we ever run out of electricity?
So yes, we will run out of electricity if we continue to rely on the burning of fossil fuels to drive transportation, power our personal energy devices, control the temperature of our homes, or run our industries. But that’s not the way our world is. Second, more of the energy you consume daily is electricity.