If you take my number, multiply it by itself, subtract 9, divide by the original number, and then add 3, you get back to my original number. What number am I?
3
Let the number be x. Following the steps: (x^2 - 9) / x + 3. This simplifies to (x - 9/x) + 3. Set this equal to x: x - 9/x + 3 = x. Subtract x from both sides: -9/x + 3 = 0, so 9/x = 3, which means x = 3.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Hard. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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