# How does this "mind probe" work?

**URL:** <https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661>\
**Category:** Factual Questions\
**Created:** [September 19, 2003, 7:37pm UTC](https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661 "2003-09-19T19:37:16Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![mala](https://avatars.discourse-cdn.com/v4/letter/m/258eb7/32.png) [@mala](https://boards.straightdope.com/u/mala)\
**Post date:** [September 19, 2003, 7:37pm UTC](https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661/1 "2003-09-19T19:37:16Z")

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I just discovered this neat little trick, but I can’t figure out how it works. I’m sure the answer is probably very obvious, but I just can’t seem to get it. Help.  
[http://www.ebaumsworld.com/mindprobe.html](http://www.ebaumsworld.com/mindprobe.html)

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**Author:** ![jack\_ss](https://avatars.discourse-cdn.com/v4/letter/j/c77e96/32.png) [@jack\_ss](https://boards.straightdope.com/u/jack_ss)\
**Post date:** [September 19, 2003, 7:41pm UTC](https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661/2 "2003-09-19T19:41:52Z")

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It didn’t work for me.

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**Author:** ![Zeldar](https://avatars.discourse-cdn.com/v4/letter/z/b77776/32.png) [@Zeldar](https://boards.straightdope.com/u/Zeldar)\
**Post date:** [September 19, 2003, 7:45pm UTC](https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661/3 "2003-09-19T19:45:49Z")

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The symbols are changed each time. The numbers in the diagonal that corresponds to multiples of 9 all have the same symbol. That’s the symbol you’ll get each time.

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**Author:** ![Doomtrain](https://avatars.discourse-cdn.com/v4/letter/d/0ea827/32.png) [@Doomtrain](https://boards.straightdope.com/u/Doomtrain)\
**Post date:** [September 19, 2003, 8:02pm UTC](https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661/4 "2003-09-19T20:02:16Z")

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Didn’t work for me, either.

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**Author:** ![Boldface\_Type](https://avatars.discourse-cdn.com/v4/letter/b/b5e925/32.png) [@Boldface\_Type](https://boards.straightdope.com/u/Boldface_Type)\
**Post date:** [September 19, 2003, 8:19pm UTC](https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661/5 "2003-09-19T20:19:04Z")

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It should always work, unless you’ve made a mistake. (Or unless the web chappies have made a mistake).

Anyway, I’ll expand **Zeldar** ’s explanation a tad:

- Any 2-digit number can be expressed as: (10a+b). I.e., 57 = (10x5+7); a=5, b=7.
- So, When you subtract each number’s digits from the number, you have: (10a+b)-a-b.
- I.e. 9a.

So, after the little manipulation, every number you end up with is a multiple of 9. If you look in the table, all such numbers have the same digit, which contains the Mystical Symbol of Great Opportunity.

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**Author:** ![panamajack](https://avatars.discourse-cdn.com/v4/letter/p/47e85d/32.png) [@panamajack](https://boards.straightdope.com/u/panamajack)\
**Post date:** [September 19, 2003, 9:21pm UTC](https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661/6 "2003-09-19T21:21:28Z")

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Maybe ‘didn’t work for me’ means the web page, since it might not be displaying correctly. I’m using Mozilla 1.4, and all I get is a small blank square where the table should be (and unless you’ve seen it before, it makes the ‘find the symbol’ instruction rather mystifying).

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**Author:** ![Capt.Ridley\_s\_Shooting\_Party](https://avatars.discourse-cdn.com/v4/letter/c/cc9497/32.png) [@Capt.Ridley\_s\_Shooting\_Party](https://boards.straightdope.com/u/Capt.Ridley_s_Shooting_Party)\
**Post date:** [September 19, 2003, 9:47pm UTC](https://boards.straightdope.com/t/how-does-this-mind-probe-work/202661/7 "2003-09-19T21:47:39Z")

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Me too.