You've probably heard this one before. If you have, then oh well. Anyways, here goes. 15 knights are riding 15 horses on a warm summer day. They approach an apple tree where coincedentally, there are 15 ripe apples. Each took an apple and ate it. How many apples are left? Hint: If the answer is 0, then it wouldn't be a very good brain teaser now would it?