If you multiply me by myself, add the number of sides on a triangle, and then divide by two, you get seven. What number am I?
Four
Let the number be x. x squared plus 3 (sides of a triangle) equals 7 times 2 (which is 14). So x squared = 11? Wait: (x^2 + 3)/2 = 7 -> x^2 + 3 = 14 -> x^2 = 11... Let's fix this math: Let the number be 4. 4 times 4 = 16. 16 plus 3 = 19? No. Let's make it work: (x^2 + 5) / 2 = 10 -> x^2 + 5 = 20 -> x^2 = 15. Let's do: (x * x + 2) / 3 = 6 -> x^2 + 2 = 18 -> x^2 = 16 -> x = 4. Let's rewrite the question to match: Multiply me by myself, add two, divide by three, and you get six. What number am I?
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: Medium. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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