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Explanation of the Mind Reader Game

The "trick" is to understand that no matter what two-digit number greater than 9 that you select, when you add the digits and subtract this sum from the two-digit number you started with, the answer MUST always be a multiple of nine -- namely, the result will be either 9, 18, 27, 36, 45, 54, 63, 72, or 81.

And if you look carefully, you'll notice that every time you try the puzzle, the symbol that corresponds to those nine numbers (9, 18, 27, 36, 45, 54, 63, 72, or 81) is always the same. The actual symbol may change each time you try the puzzle, but it will ALWAYS be exactly the same for each of those nine numbers. Thus, no matter what number you select, it will always match the symbol in the crystal ball.

To look a little deeper into the puzzle, consider the lowest two-digit number you could possibly select: 10. Ten minus 1+0 (which equals 1) is 9 (the first of the possible answers). If you picked 11 as your two-digit number, the initial number is one higher, but so is one of the digits, resulting in the same answer; for example, eleven minus 1+1 (which equals 2) is 9. This continues until you reach 20, when the process starts all over again (20 minus 2+0 or 18). Every time you reach another number ending in zero, the cycle starts all over again. To summarize: