Welcome to THIS IS MATH! a new series from math editor Vickie Kearn.

This is the first of a series of essays on interesting ways you can use math. You just may not have thought about it before but math is all around us. I hope that you will take away something from each of the forthcoming essays and that you will pass it on to someone you know.

April is Math Awareness Month and the theme this year is Mathematics, Magic, and Mystery. There is a wonderful website where you will find all kinds of videos, puzzles, games, and interesting facts about math. The homepage has a poster with 30 different images. Each day of the month, a new window will open and reveal all of the wonders for that day.

Today I am going to elaborate on something behind window 3 which is about math and card magic. You will find more magic behind another window later this month. This particular trick is from Magical Mathematics: The Mathematical Ideas that Animate Great Magic Tricks by Persi Diaconis and Ron Graham. It is a great trick and it is easy to learn. You only need any four playing cards. Take a look at the bottom card of your pack of four cards. Now remember this card and follow the directions carefully:

- Put the top card on the bottom of the packet.
- Turn the current top card face up and place it back on the top of the pack.
- Now cut the cards by putting any amount you like on the bottom of the pack.
- Take off the top two cards (keeping them together) and turn them over and place them back on top.
- Cut the cards again and then turn the top two over and place them back on top.
- Give the cards another cut and turn the top two over together and put them back on top.
- Give the cards a final cut.
- Now turn the top card over and put it on the bottom of the pack.
- Put the current top card on the bottom of the pack without turning it over.
- Finally, turn the top card over and place it back on top of the pack.
- Spread out the cards in your pack. Three will be facing one way and one in the opposite way.
- Surprise! Your card will be the one facing the opposite way.

This trick is called the Baby Hummer and was invented by magician Charles Hudson. It is a variation on a trick invented by Bob Hummer.

So where’s the math?

The math behind this trick covers 16 pages in the book mentioned above.

THIS IS MATH! will be back next week with an article on Math-Pickover Magic Squares!