Magic Trick: how?

[Boppy]

This link was sent to me recently and I fell for it. How does it work?

http://www.magictricks.co.uk/mindreader/MagicTricksMR

Give it a moment to load …

[Ponster]

Answer

Within each group of ten numbers (the teens, twenties, etc.), subtracting the sum of the two digits produces the same number: a multiple of 9. All the teens map into 9, all the twenties map into 18, all the thirties map into 27, etc. All these numbers are the same symbol; all the other symbols are scattered randomly to confuse the pattern.

This example is especially good on the internet, because the pattern can be re-arranged between trials. A different symbol each time is then used for each iteration.

[Fromage_A_Trois]

There’s only a limited number of answers - any number in the twenties will return ‘18’, anything in the thirties ‘27’ etc. You’ll notice there’s also only a limited number of symbols and - surprise! - all the numbers that are a valid solution have the same symbol (although it changes each time you try).

Drat, on preview, I see Ponster got there first.

[Boppy]

Thanks, Bras and Ponster. Now I can sleep easy.
Cheers,
B

[Ponster]

The sneaky bit is that the image with the symbols changes each time that you play !