Once upon a time, I knew a song about the Pythagorean theorem. But decades later, my high school math teacher's musical memory tool has proven…less than memorable. Fortunately, the I Used to Know That Activity Book offers a fun "summer school session" in so many of those cool facts and formulas we learned as kids but which today are gathering dust in our mental filing cabinets. Using matching games, fill-in-the-blanks, and other "quizzes," you can sharpen your homonym/ homophone skills, brush up on your Shakespeare, dabble in Venn diagrams, relearn pi, and more! We can't promise you'll be able to pass a ninth-grade geometry test with this book, but you will refresh your memory…and have fun in the process!