Interviews with Benoit Mandelbrot

This is a collection of interview clips with mathematician Benoit Mandelbrot.

https://www.webofstories.com/story/search?q=mathematician&max=10&p=1&sp=mandelbrot&ch

The interview is broken up into different topics like the Hausdorff Dimension, economics and mathematics, fixed points, and the birth of fractals.  In addition, Mandelbrot talks about his personal, academic, and professional life.  It’s an interesting window into a profoundly important person.

The website WebOfStories.com also offers clips of interviews of other scientists, like phsicists Murrary Gell-Mann and Freeman Dyson and Biologist Francis Crick.

The Terrible Trapezoid

Schoolbook ran a piece on yet another terrible test question, this one appearing on the New York State fifth grade math exam.  The most disturbing part of the situation is that no one really seems to understand just how bad this question is.

The New York Times framed the issue as requiring the student to use a technique outside the normal curriculum; the problem is worse than that.  The NYS education commissioner dismissed the error as a “typo”‘; the error can not be considered a typo.  The chancellor of the NY Board of Regents decreed that anyone who claims the tests are invalid is just pushing back against teacher evaluations; no one who understands mathematics can claim that this question is valid.

The problem starts with a trapezoid of sides 5, 16, 13, and 28.  After asking the student to find the perimeter of the trapezoid, the problem then states

A new trapezoid is formed by doubling the lengths of sides AB and CD.  Find the perimeter of the new trapezoid.

 And here’s where the trouble begins.

1)  Is this a right trapezoid?

The Schoolbook piece assumes that the trapezoid is a right trapezoid, i.e., that angle ADC is a right angle.  Nowhere in the problem is it stated or indicated that the trapezoid is right.  And even if we know that it is right, 5th graders are not expected to know the Pythagorean Theorem.

2)  Why does BC change while AD remains constant?

The Schoolbook piece also assumes that as AB and CD are doubled, the length of AD remains constant while the length of BC changes.  Thus, in order to find the new perimeter, the student must find the new length of BC (using the Pythagorean Theorem).

This is the critical error in the construction of this problem:  the test authors don’t seem to understand the subtleties of scaling figures.

Doubling AB and CD doesn’t specify a unique new trapezoid.  BC could change while AD remains constant; AD could change while BC remains constant; AD and BC could both change.  (It is interesting to note that it is impossible to double AB and CD while keeping both AD and BC constant).

Was the original intent to tell the students, or have them assume, that the angles stayed the same?  If so, the resulting figure could not exist.

Was the original intent to tell the students, or have them assume, that AD was also supposed to be doubled?  If so, this still doesn’t specify a unique new trapezoid (unless the angles also remain constant).

The concept of this problem is fundamentally flawed, and it demonstrates a real lack of mathematical understanding on the part of those who created, edited, and screened it.

What’s worse, education officials pretend that this is just a ‘typo’, and that this is no reason to question that validity of these tests.

If the consistent appearance of erroneous math questions on state exams year after year doesn’t constitute legitimate criticism of the validity of these exams, then what possibly could?

Related Posts

Visualization of Curl

This is a great visualization and explanation, of the curl of a vector field:

http://mathinsight.org/curl_idea

If you interpret a vector field as the flow of a fluid, then you can interpret the curl as a measure of the tendency to rotate at a given point.

One way to think of this is to imagine a tiny sphere, or paddle-wheel, fixed at a point in space, and then consider how that object would rotate if subjected to the flow of fluid as given by the vector field.

This write-up and series of animations from MathInsight.org are very useful in attaching some intuition to this complex idea.

Combinatorial Bracelets

This is another wonderful visual demonstration from Jason Davies:  a combinatorial bracelet generator.

http://www.jasondavies.com/necklaces/

Combinatorics is the mathematics of counting things, and one of the classic “advanced” counting problems is this:  given a certain number of beads of various colors, how many different bracelets can you make?

The problem may seem easy enough, but it becomes quite difficult when you start to understand what “different” really means.

For example, if you turn one bracelet into another by rotating it, then those two bracelets aren’t different.  Even more complicating is that if you can obtain one bracelet from another by flipping it over, then they are also the same!

This visualization can really help develop a sense of the complicated symmetries at work here.

Click here to see more in Representation.

www.MrHonner.com

Real School Reform?

Public school teachers seem to be enduring a lot of vocal criticism these days, as politicians and “reformers” call for measures that tie student performance to teacher job security.

While genuine public discourse about educational policy and philosophy should be a good thing for us all, it’s all too easy to lay the “accountability” at the feet of teachers and ignore the many other factors that contribute to student “performance”, some of which may be even more fundamental to student success.

For example, it turns out that if we provide students with healthier, more nutritious meals, they will perform better and miss less school.

http://www.guardian.co.uk/education/2011/apr/10/school-dinners-jamie-oliver

Test scores up.  Absenteeism down.  Lifetime income substantially raised.  All by replacing industrial, highly-processed cafeteria food with the real thing.

I always liked Jamie Oliver.

Follow

Get every new post delivered to your Inbox

Join other followers: