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Mind Reader: Basically a math hocus pocus


I recently downloaded a game called Mind Reader onto my Windows Phone 7 from the Marketplace. The game basically asks you to select a 2 digit number, add the two digits and then subtract the sum the of the two digits from the original number. The result is then matched against a bunch of symbols. The third step of the game then shows you the symbol associated with the number that you had arrived at post your calculations.

Now how does this work. The logic is quite simple:

The two digit number is always: x * 10 + y
The sum of the two digits is: x + y
The result after subtracting the sum from the original number is: (x*10 + y) – (x + y) = 9x

Irrespective of the number that you select, the final result will always be a multiple of 9. You will notice in the symbol grid in the application that all the multiples of 9 have the same symbol. So, if you follow the instructions given by the App, the App always get the symbol right as the final number is always a multiple of 9. As a safe measure, the symbols are always jumbled to make the logic seem a bit impossible to decipher at first.

Thanks to my friend Sourabh for locating the solution on the web after we had figured out the 9x logic.

That is all to it for getting your mind read. Smoke and mirrors, a clever math equation and some programming!