# Math Wizards, question for you (rring, rring) **URL:** \ **Category:** Factual Questions\ **Created:** [March 18, 2000, 12:52am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798 "2000-03-18T00:52:00Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![techchick68](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@techchick68](https://boards.straightdope.com/u/techchick68)\ **Post date:** [March 18, 2000, 12:52am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/1 "2000-03-18T00:52:00Z")
I am not good with numbers and wouldn’t have a clue as to how to solve this problem. It has to do with phone numbers. Given any prefix aka 719 you have 7 numbers after that to use for phone numbers. I don’t know all the rules behind phone numbers but if you start with 200-0000, and can use one and zero except in the first number, how many phone numbers can assigned under each that could be conceivable used under one area code? Does this make sense? Let me know! ---
**Author:** ![techchick68](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@techchick68](https://boards.straightdope.com/u/techchick68)\ **Post date:** [March 18, 2000, 12:54am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/2 "2000-03-18T00:54:00Z")
Oh and of course you can use any number (0-9) in the last 6 numbers, again, starting with the number 2. ---
**Author:** ![Tinker\_Grey](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tinker_grey/32/8136_2.png) [@Tinker\_Grey](https://boards.straightdope.com/u/Tinker_Grey)\ **Post date:** [March 18, 2000, 12:59am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/3 "2000-03-18T00:59:00Z")
Well, let’s see. In place of 00-0000, you can put 00-0001, 00-0002 … 00-9999 … 99-9999. In other words, all the numbers between 0 and 999,999 can be used for the 2. so for 2xx-xxxx -\> 1 million for 3xx-xxxx -\> 1 million … … \_\_\_\_\_\_\_\_\_ 8 million per area code Caveat: As long as there are no other rules. ---
**Author:** ![Arnold\_Winkelried](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@Arnold\_Winkelried](https://boards.straightdope.com/u/Arnold_Winkelried)\ **Post date:** [March 18, 2000, 1:08am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/4 "2000-03-18T01:08:00Z")
Or in other words, eight possibilities for the first digit (2-9) \* 10 possibilities to the second digit (0-9) \* 10 possibilities for the third digit … = 8 \* 10^6 = eight million ---
**Author:** ![techchick68](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@techchick68](https://boards.straightdope.com/u/techchick68)\ **Post date:** [March 18, 2000, 1:14am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/5 "2000-03-18T01:14:00Z")
Cool! Thanks! I was watching NBC Nightly News and they didn’t state how many phone numbers could be listed under each area code… So in Colorado, that’s 32 million phone number possibilities. If you divide that by 4 million, the reported amount of population (of course this doesn’t include businesses) each person then has 8 phone number possibilites? Please correct me if this is wrong…like I said, I am not good with numbers. Me? I have 3, main phone, data phone and cell phone. ---
**Author:** ![techchick68](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@techchick68](https://boards.straightdope.com/u/techchick68)\ **Post date:** [March 18, 2000, 1:21am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/6 "2000-03-18T01:21:00Z")
Now to throw in another bend, please forgive for my lack of math skills, but I would like to know how many 10 digit phone numbers is available (minus 911 and 411) Don’t call me stupid as I am stumped on this and can’t figure out what the total possibilities are. ---
**Author:** ![techchick68](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@techchick68](https://boards.straightdope.com/u/techchick68)\ **Post date:** [March 18, 2000, 1:22am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/7 "2000-03-18T01:22:00Z")
**shoot,** you have to factor in that you can’t really use 1 as the first number again, right? If there are other rules I have forgotten please factor that in and include the rule. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [March 18, 2000, 1:26am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/8 "2000-03-18T01:26:00Z")
> [@](#): > > 8 million per area code That’s a correct response to the OP but there are other limitations, right? Like 555 is directory assistance (?), and I think 9 is reserved for special numbers like 911. What other limitations are there? ---
**Author:** ![Arnold\_Winkelried](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@Arnold\_Winkelried](https://boards.straightdope.com/u/Arnold_Winkelried)\ **Post date:** [March 18, 2000, 1:29am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/9 "2000-03-18T01:29:00Z")
I assume you’re talking about phone numbers in the USA. Area codes cannot start with 0 or 1, and have three digits. (It used to be that the second digit of area codes had to be a 0 or a 1, but that is no longer true.) Phone numbers cannot start with a 0 or a 1, and always have seven digits (so that excludes those three-digit “special information” numbers.) Solution: (eight possibilities for the first digit of the area code \* 10 possibilities for the second digit of the area code \* 10 possibilities for the third digit of the area code) \* (eight possibilities for the first digit of the phone number \* 10 possibilities of the second digit of the phone number …) = 8 \* 8 \* 10^8 = 6.4 billion ---
**Author:** ![techchick68](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@techchick68](https://boards.straightdope.com/u/techchick68)\ **Post date:** [March 18, 2000, 1:35am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/10 "2000-03-18T01:35:00Z")
So, based on the population of the US, which excludes other areas that use the same number scheme (aka Canada, US Virgin Islands, etc.) there are around 274 million people, which makes it about 23.35 phone numbers per person in the US. Geez! ---
**Author:** ![Konrad](https://avatars.discourse-cdn.com/v4/letter/k/f475e1/32.png) [@Konrad](https://boards.straightdope.com/u/Konrad)\ **Post date:** [March 18, 2000, 4:40pm UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/11 "2000-03-18T16:40:00Z")
Don’t forget businesses have their own phone numbers so you’ve got to count in the lines you share at work. Also xxx-0000 and xxx-9999 are usually reserved for testing as well as some others. ---
**Author:** ![Arnold\_Winkelried](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@Arnold\_Winkelried](https://boards.straightdope.com/u/Arnold_Winkelried)\ **Post date:** [March 18, 2000, 5:14pm UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/12 "2000-03-18T17:14:00Z")
Another problem, that’s hotly debated in California, especially by people opposed to telephone overlays, is that utility commissions allocate phone numbers in blocks of 10,000 IIRC, and if a small phone service provider (e.g. cell phone company) only uses part of that block, the other ones are still unavailable. Which is why in the LA area they’re adding new area codes at the rate of one a year or so. ---
**Author:** ![WillGolfForFood](https://avatars.discourse-cdn.com/v4/letter/w/82dd89/32.png) [@WillGolfForFood](https://boards.straightdope.com/u/WillGolfForFood)\ **Post date:** [March 18, 2000, 9:56pm UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/13 "2000-03-18T21:56:00Z")
Arnold, I believe that the FCC has just modified that 10,000 value down significantly - just this week, if I’m remembering what I read in the paper right. I have to admit, though, that searching for proof of this claim on the web came up empty. ---
**Author:** ![nebuli](https://avatars.discourse-cdn.com/v4/letter/n/0ea827/32.png) [@nebuli](https://boards.straightdope.com/u/nebuli)\ **Post date:** [March 19, 2000, 3:56am UTC](https://boards.straightdope.com/t/math-wizards-question-for-you-rring-rring/8798/14 "2000-03-19T03:56:00Z")
The FCC announced the change yesterday. For details see [http://www.fcc.gov/Bureaus/Common\_Carrier/News\_Releases/2000/nrcc0018.html](http://www.fcc.gov/Bureaus/Common_Carrier/News_Releases/2000/nrcc0018.html)