How does this mathematical card trick work?

In 2016, while traveling in Finland, Manchester-based mathematician Katie Steckles was shown a mathematical card trick. It’s a self working card trick, which means that this trick automatically works because of the math involved. Follow the steps and it should always work.

Watch as Steckles demonstrates the mathematical card trick twice. She then pauses at 4m25s to give you time to figure out how it works.

The video cuts off at the end, but in the missing 12 seconds she explains that her friends at MathsJam had fun figuring out how it worked. To exercise your brain, watch the first half of the video a few times, and don’t watch the explanation from the second half of the video. Or watch it with friends and figure it out together.

Here’s a hint to get you started:

“…if you are trying to figure out how someone’s done a card trick, even if it’s a mathematical card trick—and it’s not a magician who’s doing crazy sleight of hand stuff and hiding cards at their sleeve or what have you—it is often useful to pay attention carefully to the things that they’re doing with their cards and with their hands because, quite often, there can be a clue in there.

And the first thing that I spotted when I saw this trick them was that she’s dealing from a face-up deck of cards…”

Watch these related math videos next:
• Anastasia Chavez explains the 21-card trick
• Fold & Cut Theorem: Cut any shape from only one cut
• Mental Logs number sticks, a math magic trick
• Russian Multiplication, an astonishing way to multiply
• Universal Calendar Puzzle: Figure out the day of the week for any date ever