A few years ago, I encountered two different problems in which the number 3 played surprising roles. I found myself wondering, “Why 3? What's so special about 3?” Further investigation led to continuous extensions involving exponents, logarithms, a parametric equation, maxmin problems, and some history of mathematics. As you read, pause to try the problems and play with the applets (the article's title is a big hint!)

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### Dan Kalman and Daniel J. Teague

Using ideas of Galileo and Gauss but avoiding calculus, students create a model that predicts whether a fly ball will clear the famous left-field wall at Fenway Park.

### Flor Jacqueline Alarcón Mejía

Algebra, probability, and sequences—all important curricular material—can be connected by a question that will challenge students: What is the probability *P* that the function *f*(*x*) = *x*
^{2} + *rx* + *s* has real zeros when *r* and *s* are real numbers between 0 and 9, inclusive? This problem involves an infinite sample space, making it more interesting for students who have worked on probability problems with only finite sample spaces.

### Becky Hall and Rich Giacin

Tying your teaching approach to the Common Core Standard for Geometry and Congruence will help students understand why functions behave as they do.

### Jon D. Davis

Using technology to explore the coefficients of a quadratic equation leads to an unexpected result.

### G. Patrick Vennebush, Thomas G. Edwards and S. Asli Özgün-Koca

Students analyze items from the media to answer mathematical questions related to the article. This month's clips involve finding a mathematical error in an advertisement as well as working with ratios and proportions.

### Sheldon P. Gordon

We tell students that mathematical errors should be avoided, but understanding errors is an important tool in developing numerical methods.

Readers comment on published articles or offer their own ideas.

### Lorraine M. Baron

Assessment tools–a rubric, exit slips–inform instruction, clarify expectations, and support learning.

### S. Asli Özgün-Koca

Student interviews inform us about their use of technology in multiple representations of linear functions.