Q: Why did the math book look so sad?
A: Because of all its problems.
Q: Why did the math book look so sad?
A: Because of all its problems.
Listen up, buttercup. This joke is all about wordplay. The math book is sad because it has a lot of "problems," which means both math problems AND emotional issues. Get it? I bet you didn't because you're probably bad at math too, aren't you?