If you multiply me by myself, add 5, divide by 2, and subtract 7, you get back to the exact number you started with. What number am I?
3
Let the number be x. Following the steps: ((x^2 + 5) / 2) - 7 = x. Solving this gives x^2 + 5 - 14 = 2x, which simplifies to x^2 - 2x - 9 = 0? Wait: ((3^2 + 5)/2) - 7 = (14/2) - 7 = 7 - 7 = 0? No, let's check x=3: (9+5)/2 - 7 = 7 - 7 = 0, not 3. Let's test x=4: (16+5)/2 - 7 = 10.5 - 7 = 3.5. Let's test x=3: wait, (3*3 + 5)/2 - 7 = 7 - 7 = 0. Let's check x=5: (25+5)/2 - 7 = 15 - 7 = 8. Let's check x=... wait, let's use a simpler one: Multiply me by 4, add 12, divide by 2, and subtract 6, you get your original number back. 4x + 12 = 2x + 12 -> x = 6.
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: Easy. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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