The ticket-roll as math practice

Once again today Dan Meyer’s terrific blog lends common sense and clarity to what it means to practice math at the high school level. “Mathematical notation isn’t a prerequisite for mathematical exploration,” he writes. “Mathematical notation can even deter mathematical exploration.” To illustrate, he uses a problem that starts by asking questions about a big roll of tickets:

When the textbook asks a student to “find the area of the annulus” in part (a) of the problem, there are at least two possible points of failure. One, the student doesn’t know what an “annulus” is. (Hand goes in the air.) Two, the student knows the term “annulus” but can’t connect it to its area formula. (Hand goes in the air.)

That’s the outcome of teaching the formula, notation, and vocabulary first: the sense that math is something to be remembered or forgotten but not created.

Meanwhile, let’s not kid ourselves. The area of an annulus isn’t difficult to derive. Let the student subtract the small circle from the big circle. Then mention, “by the way, this shape which you now feel like you own, mathematists call it an ‘annulus.’ Tuck that away.”

Similarly, if I give you this pattern, I know you can draw the next three pictures in the sequence. That’ll get old so I’ll ask you to describe the pattern in words. You’ll write out, “you add two tiles to the last picture every time to get the next picture.” I’ll show you how much easier it is to write out the recursive formula An+1 = An + 2. ΒΆ I’ll ask you to tell me how many tiles I’ll find on the 100th picture. You’ll get tired of adding two every time, and we’ll develop the explicit formula A = 2n + 3, which makes that task so much easier.

Terms like “explicit” and “recursive” and “annulus” can do one of two things to the exact same student: make the kid feel like a moron or make the kid feel like the master of the universe.

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One thought on “The ticket-roll as math practice

  1. Dan Meyer’s comments illustrate the debate going on now in high school mathematics. Traditionally students would be expected to memorize the area formula for the annulus and work problems calculating areas of specific examples. It is much more interesting and motivating to ask students to find out how many tickets are on the roll or how many tiles would be needed to lay out a much larger pattern. As they develop their own formulas from basic knowledge (i.e. the area of a circle) their understanding of math grows. Such practice would seem to develop much better’ habits of experts’ than the deadly drill and practice often associated with more traditional math curriculum.

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