The Question: Suppose that you have two buckets of sand, bucket A and bucket B. Bucket A contains a certain volume of pure white sand, and Bucket B contains exactly the same volume of pure black sand. Now suppose you take a teaspoon of sand from bucket A and pour it into bucket B, and stir bucket B thoroughly; then take a teaspoon of sand from bucket B and pour it back into bucket A. After doing this, does bucket A have more black sand, or does bucket B have more white sand? (i.e. which bucket has more impurities in it)?

What makes this question interesting is that there is one convincing argument that both buckets should end up with equal amounts of impurities, and another convincing argument that one bucket should have more impurities than the other. Which argument is true – and what is the logical flaw in the other argument? (I recommend that you try reaching your own conclusions first, before reading either of the two arguments).