# What is this with 9's? **URL:** \ **Category:** Factual Questions\ **Created:** [May 22, 2002, 1:09pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291 "2002-05-22T13:09:18Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![insider](https://avatars.discourse-cdn.com/v4/letter/i/bbe5ce/32.png) [@insider](https://boards.straightdope.com/u/insider)\ **Post date:** [May 22, 2002, 1:09pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/1 "2002-05-22T13:09:18Z")
How did the number 9 become so widely used for so many things: ``` Dressed to the 9's The whole 9 yards Nine lives 9 to 5 etc.? ``` ---
**Author:** ![insider](https://avatars.discourse-cdn.com/v4/letter/i/bbe5ce/32.png) [@insider](https://boards.straightdope.com/u/insider)\ **Post date:** [May 22, 2002, 1:13pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/2 "2002-05-22T13:13:55Z")
Enjoy: ``` 2x9=18 and 1+8=9 ``` 3x9=27 and 2+7=9 4x9=36 and 3+6=9 5x9=45 and 4+5=9 6x9=54 and 5+4=9 7x9=63 and 6+3=9 8x9=72 and 7+2=9 9x9=81 and 8+1=9 There are eight calculations, all ending with a 9. . . Now take the answers of the 8 calculations (all ending in 9) and times those answers by the number . of the calculations (eight) 8x9=72 and 7+2=? yes, again equaling 9 Is there any other number that will calculate in a like manner? For the answer e-mail [allen@personalsales.com](mailto:allen@personalsales.com) ---
**Author:** ![Aro](https://avatars.discourse-cdn.com/v4/letter/a/b3f665/32.png) [@Aro](https://boards.straightdope.com/u/Aro)\ **Post date:** [May 22, 2002, 1:16pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/3 "2002-05-22T13:16:55Z")
[http://www.quinion.com/words/qa/qa-nin1.htm](http://www.quinion.com/words/qa/qa-nin1.htm) [http://www.quinion.com/words/articles/nineyards.htm](http://www.quinion.com/words/articles/nineyards.htm) [http://www.uselessknowledge.com/explain/cats2.shtml](http://www.uselessknowledge.com/explain/cats2.shtml) 9 to 5 is just the standard work week. No big deal there. Don’t really see any reason to assume any connection between these sayings…just 'cause they use the number 9. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 22, 2002, 1:24pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/4 "2002-05-22T13:24:35Z")
There are all sorts of neat math tricks that can be done with all sorts of numbers. While neat and interesting I think on the whole it is meaningless. Also, If you look for them, I think you can find many other numbers that fall into our daily lexicon as well. There’s nothing weird or mystical about it. **Dressed to the 9’s** How about dressed to the ‘T’? **The whole 9 yards** Mere chance. The gun belt on a WWII plane just happened to be 9 yards long. Had it been 5 yards we’d probably all be saying “The whole 5 yards” today. **Nine lives** There probably is some myth behind this one. **9 to 5** So people happened to start at 9 a.m. as a matter of routine. Nothing there. In fact, most people I know today work 8 or 8:30 - 5 these days if they’re lucky (more if they’re unlucky). ---
**Author:** ![bordelond](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bordelond/32/150_2.png) [@bordelond](https://boards.straightdope.com/u/bordelond)\ **Post date:** [May 22, 2002, 1:31pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/5 "2002-05-22T13:31:52Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > **The whole 9 yards** > Mere chance. The gun belt on a WWII plane just happened to be 9 yards long. Had it been 5 yards we’d probably all be saying “The whole 5 yards” today. [Cecil’s famous column](http://www.straightdope.com/classics/a2_252.html) on the expression “the whole nine yards” never mentioned this possibility. Is your gun-belt origin story now generally accepted among word mavens? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 22, 2002, 1:37pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/6 "2002-05-22T13:37:54Z")
[QUOTE] \*Originally posted by Whack-a-Mole \* **The whole 9 yards** Mere chance. The gun belt on a WWII plane just happened to be 9 yards long. Had it been 5 yards we’d probably all be saying “The whole 5 yards” today. [QUOTE] yeah, or whatever the source of that particular saying really is (the book is far from closed on that issue, IIRC) The mathematical tricks with 9 are usually the basis of the ‘now multiply that by the number you first thought of’ mind-reading tricks. A lovely little tip that an accountant once showed me: If the total of a column of figures doesn’t balance, and the amount by which it differs (from what is expected) is divisible by 9 then the chances are that there is a pair of transposed adjacent digits somewhere: 123 + 234 + 345 + 456 =1158 123 + 234 + **43** 5 + 456 =1248 1248 - 1158 = 90 90 / 9 = 10 exactly. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 22, 2002, 1:54pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/7 "2002-05-22T13:54:36Z")
> [@](#): > > \*Originally posted by bordelond \* > \*\*[Cecil’s famous column](http://www.straightdope.com/classics/a2_252.html) on the expression “the whole nine yards” never mentioned this possibility. Is your gun-belt origin story now generally accepted among word mavens? \*\* The link provided by **Aro** ( [http://www.quinion.com/words/articles/nineyards.htm](http://www.quinion.com/words/articles/nineyards.htm) ) mentions it. I will admit that I had no idea the etymology of the term was so in dispute and had always used the gun belt explanation. It does look as if the gun belt is one of the slightly better ones (in that it isn’t outright debunked) but it is obviously by no means the definitive answer. > [@](#): > > Yet another explanation is that it was invented by fighter pilots in the Pacific during World War Two. It is said the .50 calibre machine gun ammunition belts in Supermarine Spitfires measured exactly 27 feet. If the pilots fired all their ammo at a target, they would say that it got “the whole nine yards”. A merit of this claim is that it would explain why the phrase only began to be recorded after the War. ---
**Author:** ![Church\_Key\_Kid](https://avatars.discourse-cdn.com/v4/letter/c/f9ae1b/32.png) [@Church\_Key\_Kid](https://boards.straightdope.com/u/Church_Key_Kid)\ **Post date:** [May 22, 2002, 2:24pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/8 "2002-05-22T14:24:31Z")
…number nine…number nine…number nine…number nine… 🙂 ---
**Author:** ![Monty](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/monty/32/47_2.png) [@Monty](https://boards.straightdope.com/u/Monty)\ **Post date:** [May 22, 2002, 2:27pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/9 "2002-05-22T14:27:58Z")
I’m wondering how it’s gotten to be in the following: [ul][li]g9good9[/ul][/li]Both meaning “good night.” Anyone know? ---
**Author:** ![Qeue](https://avatars.discourse-cdn.com/v4/letter/q/b5ac83/32.png) [@Qeue](https://boards.straightdope.com/u/Qeue)\ **Post date:** [May 22, 2002, 2:34pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/10 "2002-05-22T14:34:15Z")
Nine Hold up your hands open in front of you. Curl up any one finger and pretend that finger is a plus sign. Add up the fingers on both sides of the plus sign (curled up finger). They always add up to … 😉 ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [May 22, 2002, 2:38pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/11 "2002-05-22T14:38:17Z")
More on that mathematical trick. 9 times any integer will produce a number, the sum of the digits of which is either 9 or a multiple of 9, and you can always get back to 9 eventually. For example: 2108574968205478514 × 9 = 189771747138493066261+8+9+7+7+1+7+4+7+1+3+8+4+9+3+0+6+6+2+6 = 99 9+9 = 18 1+8 = 9 I believe that this can be derived from the fact that we use a base-10 counting system. If we used hexadecimal, then 15 would have a similar property. ---
**Author:** ![muttrox](https://avatars.discourse-cdn.com/v4/letter/m/a8b319/32.png) [@muttrox](https://boards.straightdope.com/u/muttrox)\ **Post date:** [May 22, 2002, 3:07pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/12 "2002-05-22T15:07:14Z")
To answer the actual question, just coincendince. Try counting up the sayings involving “one” or “two”. Loads more than 9. ---
**Author:** ![Swampwolf](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@Swampwolf](https://boards.straightdope.com/u/Swampwolf)\ **Post date:** [May 22, 2002, 3:34pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/13 "2002-05-22T15:34:23Z")
When I was in grade school, I remember being taught a trick to discover if **any** number of any size was divisible by 9: keep adding the digits together, and if the result was more than 10, repeat until they reach a one-digit number. If it is 9, then it’s divisible by 9. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [May 22, 2002, 3:57pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/14 "2002-05-22T15:57:41Z")
Hey, 7 ain’t no slouch either 7th Heaven Lucky 7 Throw a 7 ( a fit) 7-11 7 card stud 7 in dice 7th inning stretch ---
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [May 22, 2002, 4:00pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/15 "2002-05-22T16:00:57Z")
> [@](#): > > \*Originally posted by Achernar \* > \*\*More on that mathematical trick. 9 times any integer will produce a number, the sum of the digits of which is either 9 or a multiple of 9, and you can always get back to 9 eventually. For example: > > 2108574968205478514 × 9 = 189771747138493066261+8+9+7+7+1+7+4+7+1+3+8+4+9+3+0+6+6+2+6 = 99 > 9+9 = 18 > 1+8 = 9 > > I believe that this can be derived from the fact that we use a base-10 counting system. If we used hexadecimal, then 15 would have a similar property. \*\* Correct. You can show that any polynomial in _x_ is divisible by _x-1_ if the sum of the coefficients is. ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [May 22, 2002, 5:18pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/16 "2002-05-22T17:18:55Z")
Further, any divisor of that number will have the same property. In base 10, 3 has the property because 9 has it. In base 16, 3, 5 and 15 all have it. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [May 22, 2002, 5:30pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/17 "2002-05-22T17:30:42Z")
The adding trick works with 3, too, the key being that it is a factor of one less than the base, not just it is 1 less than the base. Or, if you like, that it leaves a remainder of 1 when dividing the base. In hexadecimal, it works for 3 and 5 as well as 15. Basically, this means that all powers of the base can be expressed as a multiple of the number in question plus 1. For a 3 digit number for instance: xyz = x_100 + y_10 + z = x\*(99+1) + y\*(9+1) + z = 99_x + 9_y + x + y +z The parts with the “9” factors divide by 3, so the whole number diveds by 3 if x+y+z does. I’m too lazy to muck about with subscript tags to do it in general form for an arbitrary base. You get the idea. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [May 22, 2002, 5:33pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/18 "2002-05-22T17:33:27Z")
whoop, simulpost. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [May 22, 2002, 5:34pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/19 "2002-05-22T17:34:36Z")
> [@](#): > > \*Originally posted by insider \* > \*\*How did the number 9 become so widely used for so many things: > > ``` > Dressed to the 9's > The whole 9 yards > Nine lives > 9 to 5 > etc.? ** > > ``` _The Penguin Dictionary of English Idioms_ lists 125 entries under Numbers, from Half to Million. There’s nothing special about 9 in the sense that you’re using it, except that you happened to think of it instead of 1, 3, or 6 or some other number. ---
**Author:** ![rjung](https://avatars.discourse-cdn.com/v4/letter/r/45deac/32.png) [@rjung](https://boards.straightdope.com/u/rjung)\ **Post date:** [May 22, 2002, 5:36pm UTC](https://boards.straightdope.com/t/what-is-this-with-9s/110291/20 "2002-05-22T17:36:49Z")
What, nobody has mentioned the Illuminati yet? After all, the Secret Masters are really big on 2s and 3s, and 3^2 = 9. It’s a conspiracy, I tell ya! 😉 [Next page](https://boards.straightdope.com/t/what-is-this-with-9s/110291.md?page=2)