# Math a Magic trick with participation **URL:** \ **Category:** Thread Games\ **Created:** [November 2, 2020, 4:42pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563 "2020-11-02T16:42:00Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Left\_Hand\_of\_Dorkness](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/left_hand_of_dorkness/32/7156_2.png) [@Left\_Hand\_of\_Dorkness](https://boards.straightdope.com/u/Left_Hand_of_Dorkness)\ **Post date:** [November 2, 2020, 5:27pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/22 "2020-11-02T17:27:49Z")
Consider, instead of asking folks to type random digits, to multiply all the digits of their phone number and all the digits of their age together. If their phone number or age includes a zero, they can skip it, or they can combine it with the immediately preceding number. So if they’re 52 and their number is 336-555-1031, they can do 5x2x3x3x6x5x5x5x1x3x1, or they can do 5x2x3x3x6x5x5x5x10x3x1 . This will be easier to understand, and should result in a pretty good spread of digits. ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 2, 2020, 5:29pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/23 "2020-11-02T17:29:40Z")
That’s a great option for a first try. But still we don’t want too many 5’s in their phone number. Someone do it with your phone number. ---
**Author:** ![Left\_Hand\_of\_Dorkness](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/left_hand_of_dorkness/32/7156_2.png) [@Left\_Hand\_of\_Dorkness](https://boards.straightdope.com/u/Left_Hand_of_Dorkness)\ **Post date:** [November 2, 2020, 5:30pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/24 "2020-11-02T17:30:24Z")
Including my age, it’s 61931x20 ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 2, 2020, 5:33pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/25 "2020-11-02T17:33:23Z")
I told you not to use a 5. 😉 I’ve got a trick for you while we’re waiting standby. ---
**Author:** ![Left\_Hand\_of\_Dorkness](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/left_hand_of_dorkness/32/7156_2.png) [@Left\_Hand\_of\_Dorkness](https://boards.straightdope.com/u/Left_Hand_of_Dorkness)\ **Post date:** [November 2, 2020, 5:34pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/26 "2020-11-02T17:34:19Z")
What? You didn’t say that. tell you what, figure out what you want the trick to be, and lemme know. This is getting a little frustrating. ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 2, 2020, 5:38pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/27 "2020-11-02T17:38:18Z")
I’m teasing. The answer is 5. I’ve got more please wait. ---
**Author:** ![Left\_Hand\_of\_Dorkness](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/left_hand_of_dorkness/32/7156_2.png) [@Left\_Hand\_of\_Dorkness](https://boards.straightdope.com/u/Left_Hand_of_Dorkness)\ **Post date:** [November 2, 2020, 5:41pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/28 "2020-11-02T17:41:09Z")
D’oh! I apologize, misunderstood you. My bad. Yes, the missing digit is 5! ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 2, 2020, 6:08pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/29 "2020-11-02T18:08:30Z")
I’ve got more but it’s a busy day at work moving furniture. If you’ve followed me here you know I like math and computers especially hex numbers like 0x80 to calculate the tropical year length. I will use 0x100-1 to calculate your Bday which you didn’t tell me. =LN(2)+5.5 Sorry only 6 digits of precision available with this old fashioned calculator I’m using. Almost your Bday. ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 2, 2020, 9:18pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/30 "2020-11-02T21:18:11Z")
I mean phone number. I mean phone number and age. You know what I meant when you type it in… ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 2, 2020, 9:20pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/31 "2020-11-02T21:20:40Z")
On the other thread we’ve been talking about 3,4,5 and e. Here we talked about 5. I can do all 8 digits of your hash. =3 \*4 \*5 +2.71827 -SIN(SQRT(5)) ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [November 10, 2020, 8:15am UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/32 "2020-11-10T08:15:01Z")
If I might gently offer some well-meaning feedback. Such a complicated set-up leaves many people unsure as to whether what you are doing is incredible or not. I could barely follow what you were asking and it seemed too convoluted to spark my interest. There may be the seed of an interesting trick there but it lacks a bit of sparkle at first pass. ---
**Author:** ![PlaceboTarget](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/placebotarget/32/1073_2.png) [@PlaceboTarget](https://boards.straightdope.com/u/PlaceboTarget)\ **Post date:** [November 10, 2020, 8:37am UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/33 "2020-11-10T08:37:08Z")
> [@Novelty\_Bobble](#): > > I could barely follow what you were asking and it seemed too convoluted to spark my interest. My impression, too. People may prefer to solve my crossword puzzle instead. 🤣 ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 10, 2020, 3:37pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/34 "2020-11-10T15:37:57Z")
It’s not that complicated. The rules are few. I only suggested some guidelines on how to choose numbers randomly. Simply: Multiply single digit numbers on your calculator Let’s try it? ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 10, 2020, 3:39pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/35 "2020-11-10T15:39:03Z")
Or do it Left Hands way (above) ---
**Author:** ![Left\_Hand\_of\_Dorkness](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/left_hand_of_dorkness/32/7156_2.png) [@Left\_Hand\_of\_Dorkness](https://boards.straightdope.com/u/Left_Hand_of_Dorkness)\ **Post date:** [November 10, 2020, 3:45pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/36 "2020-11-10T15:45:02Z")
For a little background, I teach an afterschool magic club to kids, and also teach math magic tricks as part of my math lessons for grades 3-5. A good trick is going to be foolproof, is going to have unambiguous directions, is going to walk the audience through their steps in a way that doesn’t feel onerous. If the audience can deliberately or inadvertently mess up the trick, that’s not their fault, it’s the magician’s. Try writing out your directions as numbered steps. Eliminate any places where there’s ambiguity, or where a person could accidentally mess up the trick. ---
**Author:** ![PlaceboTarget](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/placebotarget/32/1073_2.png) [@PlaceboTarget](https://boards.straightdope.com/u/PlaceboTarget)\ **Post date:** [November 10, 2020, 3:45pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/37 "2020-11-10T15:45:46Z")
It would help to provide an example of what we are supposed to do STEP BY STEP. So that everyone can understand. And then we can mimic. How about that? ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 10, 2020, 3:49pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/38 "2020-11-10T15:49:03Z")
Let’s keep it simple. Multiply single digits on your calculator. For example: 5x3x7x9x2x6x8x6x2x4… Type your answer here replacing the hundreds place with an X Try to avoid using 5 or 1 too many times. Otherwise you will end up with a bunch of 0’s at the end. ---
**Author:** ![sbright33](https://avatars.discourse-cdn.com/v4/letter/s/8e8cbc/32.png) [@sbright33](https://boards.straightdope.com/u/sbright33)\ **Post date:** [November 10, 2020, 3:51pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/39 "2020-11-10T15:51:07Z")
I appreciate your help Left Hand ---
**Author:** ![PlaceboTarget](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/placebotarget/32/1073_2.png) [@PlaceboTarget](https://boards.straightdope.com/u/PlaceboTarget)\ **Post date:** [November 10, 2020, 4:09pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/40 "2020-11-10T16:09:42Z")
When I get some time to do this, I will probably participate. So, I’m supposed to pick a one digit number, and multiply it 9 times by a one digit number at a time (without using 5 or 1 if possible). Then I’ll have to type the answer here replacing the hundreds place with an X. And you’ll guess the hundreds digit. I’ll probably try it, but it doesn’t look much of a game. It’s a kind of funny/smart trick. Can it be developed into a game? ---
**Author:** ![Left\_Hand\_of\_Dorkness](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/left_hand_of_dorkness/32/7156_2.png) [@Left\_Hand\_of\_Dorkness](https://boards.straightdope.com/u/Left_Hand_of_Dorkness)\ **Post date:** [November 10, 2020, 4:20pm UTC](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563/41 "2020-11-10T16:20:26Z")
> [@sbright33](#): > > Try to avoid using 5 or 1 too many times. Otherwise you will end up with a bunch of 0’s at the end. “too many” is ambiguous, and not an acceptable direction. You need to make this step unambiguous. Also, “1” won’t have this effect, but “0” will. Consider changing the direction: “Don’t use 0 or 5.” [Previous page](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563.md?page=1) [Next page](https://boards.straightdope.com/t/math-a-magic-trick-with-participation/924563.md?page=3)