Math textbooks might be boring, but can a math textbook with cat pictures be boring? I don’t think so! Sheldon Axler is a funny math professor at San Francisco State University, and he put his cats’ pictures into his math textbook, Precalculus: A Prelude to Calculus. You can get his book here.

Here is the question about his cat: Suppose a cat skeleton found in an old well has a ratio of carbon-14 to carbon-12, which is 61% of the corresponding ratio for living organisms. Approximately how long ago did the cat die?