Get smart curated videos delivered to your inbox.   SUBSCRIBE
The Kid Should See This

Anastasia Chavez explains the 21-card trick

Watch more with these video collections:

How can you use math to astonish your friends and family? Try the 21-card trick. Filmed for Numberphile, UC Davis Department of Mathematics Postdoc Anastasia Chavez demonstrates step-by-step how this trick works with the help of some simple math.

Anastasia Chavez
21 card trick
And if you like that one, try this slightly more complex 27 card variation, as demonstrated by mathematician Matt Parker:

Watch more Numberphile and more with Matt Parker including:
An unexpected way to inflate a balloon
The Fold & Cut Theorem
The Brick Double-Domino Effect Explained

Plus: How to multiply numbers by drawing lines and Universal Calendar Puzzle: Figure out the day of the week for any date ever.

This Webby award-winning video collection exists to help teachers, librarians, and families spark kid wonder and curiosity. TKSST features smarter, more meaningful content than what's usually served up by YouTube's algorithms, and amplifies the creators who make that content.

Curated, kid-friendly, independently-published. Support this mission by becoming a sustaining member today.