Wrapped Trapezoid

Wrapping up this gift was much more challenging than I expected.

But it got me thinking about how this could be an interesting project.  Questions such as “What’s the smallest square piece of wrapping paper that could do the job?” or “What kind of rectangle would work best?” are compelling and  easy to investigate.  And maybe someone could make a triangle or trapezoid do the job efficiently.  There’s a lot of room for creativity and exploration here.

The usual restrictions on tearing and cutting would apply, although relaxing those restrictions might create interesting problems, too.

It wasn’t easy, but I did pick up some unexpected ideas along the way.  And the gift was well-received, too!

Are These Tests Any Good? Part 2

This is the second entry in a series that examines the test quality of the New York State Math Regents Exams.  In the on-going debate about using student test scores to evaluate teachers (and schools, and the students themselves), the issue of test quality rarely comes up.  And the issue is crucial:  if the tests are ill-conceived, poorly constructed, and erroneous, how legitimate can they be as measures of teaching and learning?

In Part 1 of this series I looked at three questions that demonstrated a significant lack of mathematical understanding on the part of the exam writers.  Here, in Part 2, I will look at three examples of poorly designed questions.

The first is from the 2011 Integrated Algebra Regents:  how many different ways can five books be arranged on a shelf?

This simple question looks innocent enough, and I imagine most students would get it “right”.  Unfortunately, they’ll get it “right,” not by answering the question that’s been posed, but by answering the question the exam writers meant to ask.

How many different ways are there to arrange five books on a shelf?  A lot.  You can stack them vertically, horizontally, diagonally.  You can put them in different orders; you can have the spines facing out, or in.  You could stand them up like little tents.  You could arrange each book in a different way.  The correct answer to this question is probably “as many ways as you could possibly imagine”.  In fact, exploring this question in an open-ended, creative way might actually be fun, and mathematically compelling to boot.

But students are trained to turn off their creativity and give the answer that the tester wants to hear.  A skilled test-taker sees “How many ways can five books be arranged on a shelf?” and translates it into  “If I ignore everything I know about books and bookshelves, stand all the books upright in the normal way, don’t rotate, turn or otherwise deviate from how books in math problems are supposed to behave, then how many ways can I arrange them?”

This question is only partly assessing the student’s ability to identify and count permutations.  This question mostly tests whether the student understands what “normal” math problems are supposed to look like.

This problem is an ineffective assessment tool, but there’s something even worse about it.  Problems like this, of which there are many, teach students a terrible lesson:  thinking creatively will get you into trouble.  This is not something we want to be teaching.

Here’s a question from the 2011 Algebra II and Trigonometry exam:

Solving equations is one of the most important skills in math, and this question pertains to a particular method (completing the square) used to solve a particular kind of equation (quadratic).  But instead of simply asking the student to solve the problem using this method, the question asks something like “if this procedure is executed normally, what number will be written down in step four?”.

This is not testing the student’s ability to do math; instead, it’s testing whether or not they understand what “normal” math looks like.  There are many ways to solve equations, and there are many ways a student might use this method.  Whether it looks exactly like what the teacher did, or what the book did, isn’t especially relevant.  So why is that being tested?  And like the question above, this reinforces the idea that thinking creatively can be dangerous by insisting that students see the “normal” solution as the only correct one.

Finally, here’s a problem from the 2011 Geometry Regents:

Once again, the student is not being tested on their knowledge of a concept or on their ability to perform a task.  Instead, they’re being tested on whether or not they recognize what “normal” math looks like, and that’s just not something worth testing.  There are lots of legitimate ways to construct a perpendicular bisector:  why are we testing whether the student recognizes if the “normal” way has been used?

These three problems showcase some of the dangers inherent in standardized testing.  Questions like these, and the tests built from them, discourage creative thinking;  they send students the message that there is only one right way to do things; they reinforce the idea that the “correct” answer is whatever the tester, or teacher, wants to hear; and they de-emphasize real skills and understanding.

At their worst, these tests may not just be poor measures of real learning and teaching; they may actually be an obstacle to real learning and teaching.

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Library of Curves

Witch of AgnesiThis is a nice resource:  a Famous Curves Index, provided by the School of Math and Statistics at the University of St. Andrews, Scotland.

http://www-history.mcs.st-and.ac.uk/Curves/Curves.html

You can view graphs of the tractrix, Fermat’s Spiral, and Quadratrix of Hippias, and see their various algebraic representations.  Each entry in the Curve Index contains a brief history of the curve, some interesting facts, and links to other related curves.

This collection is similar to another fun resource provided by the same program:  a comprehensive on-line library of biographies of mathematicians.

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A Good Math Story

This video lecture from the Princeton Public lecture series features psychologist Stanislas Dehaene and mathematician and author Steven Strogatz discussing math, learning, and teaching.

Dehaene, a leading researcher in how the brain acquires and processes mathematical knowledge, has some interesting things to say about whether mathematics is innate or learned.  He also describes some fascinating research conducted on number sense and geometric understanding in primitive societies.

What I enjoyed most in this lecture, however, are the two stories from Steven Strogatz about his personal experiences learning math.  At around the 23:30 mark, Strogatz tells the story of when he first became “really interested” in math.  Strogatz is a wonderful storyteller, and the tale should resonate with anyone who has discovered, or is discovering, their passion for math or science.

Strogatz’s second story is about his first experience being “weeded out” in an advanced math course in college.  This is a story I wish I had heard as a student, and it’s something I’ll definitely be sharing with my students from now on.

And for more on math and teaching from Professor Strogatz, check out how his book “The Calculus of Friendship” is a great read for advanced math students.

Fun With Fractals

I love spending time with my niece and nephew.  They are inquisitive, thoughtful, energetic, fun, and always up for anything.  As math is often on my mind, mathematical ideas often come up when we’re together.  I love exploring math with them:  we talk about numbers, ponder questions, play with shapes, estimate things.  They usually enjoy it, and if they don’t, they don’t mind telling me so.  Just like the rest of my students.

The last time I was in the neighborhood, I stopped by to see if they were around.  They weren’t home, but a I saw a piece of chalk lying on the ground.  I scribbled a quick note in the driveway letting them know I’d been by.  Before I knew it, a little triangle had appeared under my message.

When I came back later, there were many questions to answer about the mysterious diagram (it’s not the first time such triangles have appeared unexpectedly).  I told them a chilling tale about Waclaw Sierpinski, and then showed them how to make their own Sierpinski Triangle:  draw any triangle; find the midpoints of the sides; connect; repeat!  Soon, we were drawing triangles all over the neighborhood.

 An unprompted pentagon even appeared!

After lots of drawing, lots of questions, and a triangle scavenger hunt, it was time to go.  Another fun afternoon spent with my niece and nephew, and I left impressed, as I usually do.  And hopeful, too, that maybe one day my niece will actually admit that she likes math!

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