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March 2006 Contents

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ARTICLES

**Truck Drivers, a Straw, and Two Glasses of Water**

*Kevin Iga and Kendra Killpatrick*

82-92

While waiting for his meal to arrive, a truck driver was using his straw to move water from one glass to another when he was struck by this question: If I keep doing this, will the two glasses ever have exactly the same amount of water? This article looks at various problems related to that question.

**Straw in a Box**

*Richard Jerrard, Joel Schneider, Ralph Smallberg, and John Wetzel*

93-102

A problem on a state's high school exit exam asked for the longest straw that would fit in a box. The examiners apparently wanted the length of a diagonal of the box, but the figure accompanying the question suggested otherwise — that the radius of the straw be considered. This article explores that more general problem.

**A Card Trick and the Mathematics Behind It**

*Gabriela R. Sanchis*

103-109

We describe a card trick in which the magician is able to identify correctly a card chosen randomly from an array of cards by a member of the audience. We then explore the mathematics behind the trick.

**No Arithmetic Cyclic Quadrilaterals**

*Raymond A. Beauregard*

110-113

A quadrilateral is arithmetic if its area is an integer and its sides are integers in an arithmetic progression, and it is cyclic if it can be inscribed in a circle. The author shows that no quadrilateral is both arithmetic and cyclic.

**Folding Beauties**

*Leah Wrenn Berman*

**How to View a Flatland Painting**

*Mark Schlatter*

114-120

Using the problem of determining where a Flatland artist was standing, this article takes another look at perspective.

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Fallacies, Flaws, and Flimflam

*Ed Barbeau, editor* 121-124

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Classroom Capsules

*Michael Kinyon, editor*

125-142

**The Birthday Problem Revisited**

*Eric Maim, Gail Nord, James Colin Hill, and John Nord*

125-128

The birthday problem considered here is that of having been born on a specific date, say January 1, not just one person, but precisely *k* in a group of *n*. Extending the probability to being continuous through the use of the gamma function leads to an interesting surface.
**A Geometric Look at Sequences that Converge to Euler's Constant**

*Duane W. DeTemple*

128-131

In this note, the author generates and then investigates further some sequences that converge to Euler's constant.

**Partial Fraction Decomposition by Division**

*Sidney H. Kung*

132-134

The author shows how division can be used to find the partial fraction decomposition of a rational function whose denominator is either a power of a linear function or a power of an irreducible quadratic.

**An Elegant Mode for Determining the Mode**

*D.S. Broca*

134-137

A method first proposed by N.A. Rahman uses the logarithm and the derivative to find the mode. The technique is illustrated for three skewed density functions, the extreme value, the Weiball, and the lognormal.

**Searching for Möbius**

*Al Cuoco*

137-142

This capsule shows the Möbius function arises through the algebra of formal Dirichlet series.

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Problems and Solutions

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Media Highlights

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Book Reviews

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George Pólya Winners