# Anyone good with 'general rules' ?

• Mar 6th 2013, 10:03 AM
Glyn
Anyone good with 'general rules' ?
Hi - i've just watched a youtube magic card trick - { Math magic card trick!! - YouTube } - although I understand the math involved - i'm stuck trying to define a 'general rule' or formula to describe the exercise. Can anyone please help or advise ?
• Mar 7th 2013, 04:00 AM
jackkaries
Re: Anyone good with 'general rules' ?

I just join this forum and I really appreciate your work. This trick is awesome and I will try this one as soon as possible .

lists
• Mar 7th 2013, 05:49 AM
HallsofIvy
Re: Anyone good with 'general rules' ?
As a general rule, there are no "general rules".
• Mar 7th 2013, 06:00 AM
Glyn
Re: Anyone good with 'general rules' ?
Many thanks ! I just wondered, with both 52 and 10 being limiting factors in the exercise, whether there was an expression that could be used to describe the use of the exercise.
• Mar 7th 2013, 09:13 AM
BobP
Re: Anyone good with 'general rules' ?
I'm not sure what is meant by a ' general rule ', but if it's simply the maths behind this trick, that's pretty easy.

First note that if you know the bottom card of a pile, then you know how many cards there are in the pile, simply subtract from 11.
If for example the bottom card is a 4, then you count 4,5,6,7,8,9,10. That's 7 cards and equals 11 - 4.

Suppose then that the bottom cards of the three chosen piles are a, b and c.
The total number of cards in the three piles will be (11 - a) + (11 - b) + (11 - c) = 33 - (a + b + c), in which case the number of remaining cards will be 52 - {33 - (a + b + c)} = 19 + (a + b + c).
Subract 19 and you are left with (a + b + c), the sum of the bottom cards in the three piles.
• Mar 7th 2013, 04:44 PM
Glyn
Re: Anyone good with 'general rules' ?
Many thanks. I simply wondered if there were a more succinct expression than 52 = 19 + remainder stack + stacks a+b+c.
• Mar 8th 2013, 12:17 AM
BobP
Re: Anyone good with 'general rules' ?
I'm still not sure what it is that are looking for. It's easy enough to extend this to multiple packs, multiple stacks and a different top number (<=13), but it would seem that you are always going to arrive at some formula of this type.
• Mar 9th 2013, 03:21 AM
Glyn
Re: Anyone good with 'general rules' ?
Thank you for the reply - I have resolved the math - just wondered if there were any suggestions about encapsulating this exercise in a simple and engaging algebraic model for teaching children