Math Magic: The Index Card Trick

This simple trick with an index card shows kids that anything is possible!

By Sarah Hauge, Publisher of Macaroni Kid Englewood, Greenwood Village, Centennial, Colo. July 9, 2020

One of the most common questions inventors ask themselves is whether or not an idea is possible. 

During a summer home from college, I had the chance to co-teach a summer camp class called "Inventor's Workshop" at the Tech Museum in San Jose, Calif. -- one of the coolest jobs ever!

I found a simple index card test was a great way to show my brilliant third- and fourth-grade students that even an idea that might seem impossible can actually be accomplished if you think about the challenge in a new and different way. This simple trick showed the kids that with a little thought and creativity, they can accomplish anything.

The index card test

Using only a pair of scissors, can you cut a hole in an index card such that you can fit your entire body through it? The paper must form a continuous loop. No tape or glue is allowed.

Supplies needed:

  • Index card
  • Scissors

Is it possible?

Have you given it a try? What's working? What isn't? It might seem like an impossible test, but it really is possible to complete this task! Below is a step-by-step guide to solving the problem in just ONE way -- but I challenge you to keep looking for more solutions! 

  1. Fold your index card in half.
  2. Cut alternating slits in the index card, starting on the folded edge. The green lines in the image below illustrate this step.
  3. Open the index card and carefully cut straight through the middle core, as shown in the photo below. Do NOT cut the first or last strips of paper.
  4. Stretch the paper open and step through the hole you've created!


Want to take the challenge one step further? See how BIG your circle can get! Can you fit two people inside a circle created from an index card? How about 4? Here's a hint: The closer you cut your slits, the bigger your circle will get.

This simple trick shows that when it comes to big ideas, nothing is truly impossible. Push your creativity, test your imagination, and your ideas will come to life!

Sarah Hauge is the publisher of Macaroni Kid Englewood, Greenwood Village, Centennial, Colo.