Colm MulMathematics professor Colm Mulcahy, Ph.D.,  may not be a jack of all trades, but he is certainly a master of many tricks. Mathematical card tricks, that is. Widely known as “Card Colm” in academic and recreational mathematics circles, Dr. Mulcahy is now celebrating the recent release of his new book, Mathematical Card Magic: Fifty-Two New Effects. Boasting 80 percent original content, the book provides an entertaining look at mathematically based card tricks.

As the first Spelman mathematics professor to author a book, Dr. Mulcahy remains a committed academician who combines math and magic to peak people’s interest in mathematics.

“It makes math fun,” said Dr. Mulcahy, flashing an infectious smile and wearing a whimsical black tie emblazoned with playing cards. “Math and magic can be used to make people interested in mathematics. Recreational math engages people. You can attract people ages 8 to 80, and you get them involved.”

Mathemagic with a Deck of Cards

Born and raised in Dublin, Ireland, Dr. Mulcahy began his Spelman teaching career in 1988. In 1999, he met Paul Zorn, former president of the Mathematical Association of America, who turned him on to the concept of mathematical card tricks. Zorn shared the “five-card trick,” in which someone is given any five cards from a deck, and shows you only four of them. You have to figure out what the last one is.

It took him three days to crack the code. He was hooked and started seeking out other tricks in the genre, and soon he was inventing his own.

“I immediately started using those in class to motivate students, and here we are 14 years later,” said Dr. Mulcahy, who in the spring was promoted to full professor, and recently received the 2013 Senior Faculty Scholarship Award.

To understand his passion for math tricks, one only needs to witness Dr. Mulcahy in action.

In the ice cream trick, a spectator is asked to shuffle the cards and call out the name of her favorite ice cream flavor, which happens to be chocolate. Next, she cuts off about a quarter of the deck and holds it ready for dealing. Dr. Mulcahy then takes another quarter of the deck and demonstrates a spelling deal, dealing cards into a pile, one for each letter in the word “chocolate,” before dropping the rest of the quarter deck on top. Those cards are set aside and the spectator then performs this spelling routine three times with the cards in her hands. To her surprise, Dr. Mulcahy correctly names the top card in her pile at the conclusion of her triple dealing.

Another trick he invented is “Little Fibs,” named for his use of Fibonacci numbers, which is a series of numbers in which each number is the sum of the two preceding numbers, such as 1, 2, 3, 5, 8, 13, etc. In this trick, a spectator picks two cards and reports only on the total of their values. Dr. Mulcahy then names each card, value and suit. He created the trick in 2008 while teaching Math 193, a quantitative reasoning course for first-year students in the Honors Program.

“I thought I could get a mathemagic trick out of them, and it was the coolest thing.”

Math Tricks Have Purpose

Dr. Mulcahy loves introducing new mathematical card tricks to his students at the beginning of each semester. Whether he’s teaching pre-calculus, algebra, geometry, consumer mathematics or quantitative reasoning, the tricks help him break the ice and make a connection.

Just ask history major Andrea Kinzer, C’2015, who took his contemporary mathematics class.

“I loved his magic tricks,” said Kinzer . “He usually incorporated his tricks with a deck of cards when we learned about probability. His tricks honestly didn’t cease to amaze me. In many ways, it gives visual learners an opportunity to see probability examples and learn for themselves in a simpler way.”

Biology major Beryl Oluch, C’2016, agreed.

“He was good at explaining concepts,” said Oluch, who took Dr. Mulcahy’s pre-calculus class. ”His math tricks were helpful because when we did a problem, he gave us a math trick to make sure we understood the math concept.”

Dr. Mulcahy notes that his math tricks have purpose.

“It’s not just entertaining,” said Dr. Mulcahy, who blogs for the Huffington Post and MAA. His puzzles have even appeared in the New York Times. “These tricks can lead to application years later. There’s a recent use of card shuffling math to data compression. You never know where things are going to lead.”

Jeff Ehme, Ph.D., professor and chair of mathematics, praised his colleague as an inventive and clever professor who’s known for incorporating real-world application to his classes.

“He’s extremely demanding,” Dr. Ehme said. “He sets the highest standards and won’t compromise or make things easy. He expects his students to meet the challenge.”

Dr. Mulcahy has also set challenges for himself. While on leave from Spelman this academic year, he plans to spend time pursuing other writing projects and will also assist with organizing a national mathematics awareness month initiative.

“I’m a multitasker,” he said. “The traditional boundaries between teaching and research and service have become blurred for me over the past 10 years. Spelman has fostered such a flexible and supportive working environment. For that, I’m grateful.” – Alicia Lurry is senior communications specialist and editor of the Spelman Connection for the Office of Communications.