Here’s a quick puzzle that looks almost too easy: A box has 900 balls. Ninety percent are red. How many are not red? Most people answer immediately, and this time, the obvious answer really is the correct one. If 90% are red, the remaining 10% are not red.

Now calculate 10% of 900. Divide 900 by 10 and you get 90. You can check it another way: 90% of 900 equals 810 red balls, and 900 minus 810 leaves 90 balls that are not red. Simple, right? But this puzzle becomes interesting when you start questioning the wording rather than the math.

The sentence doesn’t tell us what colors the remaining balls are, but that doesn’t change the calculation. If 90% are red, then exactly 10% must be something other than red. Some playful puzzle-solvers might try to argue that all 900 balls could somehow be red, making the answer zero—but that would contradict the original statement because then 100% would be red, not 90%.

So there’s really only one mathematically correct answer: 90 balls are not red. The alternative “0” is simply a creative what-if scenario that changes the information given in the puzzle. Did you get 90 right away, or did you start looking for a hidden trick? Sometimes the simplest puzzles are the ones that make us question our assumptions the most!