Here’s a quick puzzle that looks almost too easy at first: A box contains 900 balls, and 90% of them are red. How many are not red? Most people can solve it almost instantly, and in this case, the obvious answer really is the correct one. If 90% of the balls are red, then the remaining 10% must be a different color.

To find 10% of 900, simply divide 900 by 10, which gives you 90. Another way to confirm the result is to calculate 90% of 900, which equals 810 red balls. Subtracting those 810 red balls from the total of 900 leaves exactly 90 balls that are not red.

The wording may encourage some puzzle-solvers to look for a hidden trick, but there really isn’t one. We are not told what colors the remaining balls are, but that information is unnecessary. As long as 90% of the balls are red, the other 10% cannot be red. Saying that all 900 balls are red would contradict the original statement because that would mean 100% are red.

Therefore, the mathematically correct answer is 90 balls that are not red. Did you get the answer immediately, or did you start searching for a trick? Sometimes the simplest puzzles can make us second-guess ourselves simply because the solution seems almost too obvious.