Can you count the number of rectangles in the grid? How about in the L-shaped grid? These problems appeared on the TV show Superhuman hosted by Kal Penn (Kalpen Modi). The contestant Summer gave the correct answer to each challenge in about 10 seconds. It would seem you have to be a savant to count the possibilities so quickly. But in fact anyone can solve the problems with the "super power" of mathematics. In this video I explain a mathematical method for counting rectangles.

By request, here is a version of the video at 88 percent opacity (slightly grey text, like YouTube's dark theme), but I do not think it looks as nice:
https://youtu.be/HHbARmoEfdY

My blog post for this video:
https://wp.me/p6aMk-5j8

Superhuman TV Show Rectangled Challenge (contains spoiler of the answer--avoid watching if you want to solve it first!)
https://www.youtube.com/watch?v=EyLZByxvwZ4

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My Books

"The Joy of Game Theory" shows how you can use math to out-think your competition. (rated 3.8/5 stars on 30 reviews) https://www.amazon.com/gp/product/1500497444

"The Irrationality Illusion: How To Make Smart Decisions And Overcome Bias" is a handbook that explains the many ways we are biased about decision-making and offers techniques to make smart decisions. (rated 5/5 stars on 2 reviews) https://www.amazon.com/gp/product/1523231467/

"Math Puzzles Volume 1" features classic brain teasers and riddles with complete solutions for problems in counting, geometry, probability, and game theory. Volume 1 is rated 4.4/5 stars on 13 reviews. https://www.amazon.com/gp/product/1517421624/

"Math Puzzles Volume 2" is a sequel book with more great problems. (rated 5/5 stars on 3 reviews) https://www.amazon.com/gp/product/1517531624/

"Math Puzzles Volume 3" is the third in the series. (rated 3.8/5 stars on 4 reviews) https://www.amazon.com/gp/product/1517596351/

"40 Paradoxes in Logic, Probability, and Game Theory" contains thought-provoking and counter-intuitive results. (rated 4.3/5 stars on 12 reviews) https://www.amazon.com/gp/product/1517319307/

"The Best Mental Math Tricks" teaches how you can look like a math genius by solving problems in your head (rated 4.7/5 stars on 4 reviews) https://www.amazon.com/gp/product/150779651X/

"Multiply Numbers By Drawing Lines" This book is a reference guide for my video that has over 1 million views on a geometric method to multiply numbers. (rated 5/5 stars on 3 reviews) https://www.amazon.com/gp/product/1500866148/