How does the mystic ball work?!?

Question

http://www.bored.com/mysticalball/index.htm

ok i am trying to explain it to my friend i keep telling her and shes just not getting it can any one help me explaine it to her because i keep telling her and shes not getting it can it be any simpler please try to do this in lamens term thank you very much

Answer 1

This is one of those cases where the mathematics looks random, but it really isn't.  The calculation forces you to pick a specific symbol, even though you're given the illusion of having free choice.  There are lots of magic tricks based on this idea.  

Basically, when you pick a double-digit number and do the calculation, you ALWAYS get a multiple of 9, regardless of what number you start with.  If you look closely at the chart, you'll noticed that all multiples of 9 (9, 18, 27, 36, 45, 54, 63, etc. except for 99) have the same symbol.

The symbols all change when you reload the page, but again, all multiples of 9 will be the same symbol.  This forces you the pick the same symbol.  This is how the Mind Reader "knows" what you're going to pick.

To go beyond layman's terms, here is a formal but short mathematical proof of how choosing any 2 digit number, then subtracting the sum of its digits, will always give you a multiple of 9:

Let "A" be the first digit, and "B" be the second digit.  Then the number itself has a value of 10A+B.  The sum of the digits is A+B.  Subtracting this gives 10A+B - (A+B) = 10A + B - A - B = 9A, which is 9 times a single digit and thus a multiple of 9.  Note that you can never get 99 from this, even though it is a multiple of 9, so it's OK that #99 has a different symbol since there's no calculation that will pick it.

Answer 2

idk, but i just did it and i want to know too now.

Answer 3

lol...it didn't work for me... :)