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Colm Mulcahy
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Mathematician Colm Mulcahy's latest book is Mathematical Card Magic from AK Peters/CRC Press.

He earned a B.Sc. and M.Sc. from University College Dublin, in his native Ireland, and then a PhD from Cornell University. He's Professor of Mathematics at Spelman College, in Atlanta, Georgia, where he's been teaching since 1988. He's currently visiting American University in DC.

His mathematical interests are broad, and he is a recipient of the Mathematical Association of America's Allendoerfer Award for excellence in expository writing. He’s been publishing original mathematical card trick principles bi-monthly at MAA.org since 2004, and other puzzles of his have appeared in the New York Times. He also blogs as "Maths Colm" at Aperiodical and tweets as @CardColm.


He was fortunate to know Martin Gardner for the last decade of his life.

Entries by Colm Mulcahy

Mathematics, Magic and Mystery

(1) Comments | Posted April 30, 2014 | 8:10 PM

Mathematics is all about numbers and number crunching, right? Actually, no, only part of it is. (In general, number crunching is more accurately identified with the domains of business, accountancy or engineering.)

Mathematics is more about curiosity, logic, patterns and beauty, and also has its share of delicious surprise, wonder,...

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Magical History Tour -- and Your Fave Fab Four Album Is in the Cards

(0) Comments | Posted February 7, 2014 | 2:11 PM

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Main Entry Image

Paul McCartney, George Harrison, John Lennon (vorne v.l.) und Ringo Starr (hinten) von der englischen Band The Beatles treten in New York, USA, in der TV-Sendung "Ed...

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Martin Gardner -- The Best Friend Mathematics Ever Had

(21) Comments | Posted October 20, 2013 | 7:18 PM

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What do L. Ron Hubbard, H.G. Wells, G.K. Chesterton, Lord Dunsany, Alice in Wonderland, M.C. Escher, John H. Conway, Roger Penrose and Oprah Winfrey have in common? The same thing as Isaac Asimov, Vladimir Nabokov, and Salvador Dali. And the vase illusion shown, which was designed...

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Getting Kids Excited About Mathematics, One Festival at a Time

(0) Comments | Posted July 11, 2013 | 4:00 PM

It was a beautiful May morning, and McCaw Hall in the Arrillaga Alumni Center at Stanford University was jam packed and buzzing with excitement. About 250 youngsters aged 7 to 17 had come in search of challenges and thrills, and they weren't disappointed by the festive atmosphere and friendly vibe.

...
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What Do I Have to Do to Get an A in This Class? (A Mathematical Perspective)

(1) Comments | Posted April 30, 2013 | 6:07 PM

It's that time of the year again. Final exams in colleges and universities are getting close, and one of the most popular questions students are asking their instructors is, "What do I have to do to get an A in this class?" (In other cases it may be, "What do...

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Centenary of Mathematician Paul Erdős -- Source of Bacon Number Concept

(0) Comments | Posted March 26, 2013 | 11:04 AM

In recent years many people have had fun attributing Bacon numbers to actors, reflecting how far removed from working with Kevin Bacon they are. Edward Asner has Bacon number 1 as he made a movie with Bacon, and Elvis Presley had Bacon number 2 (having been in an...

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In My Heart of Hearts: Valentine's Day Special

(0) Comments | Posted February 14, 2013 | 8:14 AM

Just in time for Valentine's Day, a magical romantic experience for all lovers (of cards), thanks to the power of mathematics.

Take out a deck of cards and extract the thirteen Hearts, setting the rest aside. Deal the Hearts into a heart-shaped display, something like as shown. There is no...

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The Role of Biking and Hiking in Mathematics

(3) Comments | Posted February 1, 2013 | 10:00 AM

In my last post, I discussed the less-obvious role of mathematics in answering simple questions about biking. What about the role of biking (or hiking) in answering difficult questions about mathematics?

Many people who run, hike or bike long distances have noticed that these activities...

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Mean Questions With Harmonious Answers

(3) Comments | Posted January 18, 2013 | 5:20 PM


2013-01-15-TucsonCU.jpgAodh and Bea each biked half of a 180-kilometer fundraiser race, in that order, as a relay team. His average speed was 36 kilometers per hour, and hers was 20 kilometers per hour. What was their average speed overall?

They shared the task...

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A Pound of Quarters vs. a Pound of Dimes: Which Is Heavier, and Which Is Worth More?

(9) Comments | Posted January 2, 2013 | 12:38 PM


2012-12-28-Balance2.jpgMany youngsters have heard, and perhaps even fallen for, the classic teaser: "Which is heavier: a ton of bricks or a ton of feathers?"

The juxstaposition of the words "brick" and "feather," in the context of weight, serves as perfect misdirection. It catches a...

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Flipping Miracles (or Bar Bets to Amaze Your Friends)

(6) Comments | Posted December 14, 2012 | 5:30 PM


Do you like a little cream in your coffee, or are you one of those people who likes a little coffee in your cream?

In front of you is a pot of coffee and a jug of cream.

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You transfer one teaspoon...

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Ratio: A Recurring Theme in Food, Art and Graphics

(2) Comments | Posted November 29, 2012 | 4:13 PM

Thinking about food can sometimes lead to artistic and mathematical insight. As with many things in life, especially those involving taste or sight, it's all a matter of proportion and balance.

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Vermeer's "The Music Lesson" (c. 1665)

Last time...

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Oranges and Apples Comparisons: The Roots of the Problem

(6) Comments | Posted November 9, 2012 | 9:55 AM

Can you think of a shape that occupies three times as much area on a page as it used to, when it's doubled in size? We'll provide a flaky answer later on.

Did you know that to check the accuracy of claims such as "he's twice the man...

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Weak Math? Try Math Week!

(18) Comments | Posted October 25, 2012 | 1:42 PM

When is the last time you went to a party and somebody boasted of being inarticulate, illiterate, or socially stunted? You probably can't remember.

Yet, those of us who work with mathematics daily are all too familiar with the scenario of truthfully answering the query "What do you do?"...

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Food for Thought: Savory Treats for the Mind From the Julia Child of Mathematics and Rationality

(1) Comments | Posted October 10, 2012 | 6:47 PM

It's not that common to become a revered national figure for over four decades in a field in which you had no formal training, having not started till you were essentially middle-aged. And then to influence a generation (or two) of enthusiasts to the extent that many ended up pursuing...

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