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Playlist: AC Favorites

Broken Calculator: 2-Digit Subtraction

This calculator gets subtraction wrong the same way every time. Can your students crack its broken rule?

Math Curiosity: Magic Squares

Imagine a 3×3 square in which every row, column, and diagonal have the same sum. That’s a magic square!

Place Value (Beyond Base 10)

Place value is something we cover in elementary school. It seems simple, but I’d wager that very few adults really understand the topic. I sure didn’t until I worked with non-base-10 number systems in college. Your students can get a taste of this mind-boggling experience by imagining what it would be like if we didn’t have the number 9. What would each digit represent then?