Sunday, March 30, 2014

Linkfest for Sunday, March 30

Friday, March 28, 2014

Guest Post: John Spencer Addresses "Frustrated Parent"

John's was the first post I saw about the silly complaint going around from "Frustrated Parent". (Now I've seen about three more. They all have good things to say.) John has graciously allowed me to share his whole post here. (But the comments over at his place are an interesting mix, so go on over there too.) Here's John:

There are many things I hate about the Common Core standards. I hate the way teachers were pushed out of the creation and adoption phase and how we have little voice in the implementation. I hate the fact that the standards will continue to be assessed with standardized, multiple choice tests and that these scores will be used with Value Added Measures in both teacher salary and teacher evaluation. However, I think it's important that in our criticism of bad policy we are careful to avoid blasting good pedagogy.

I'm seeing many of these posts making their rounds on Facebook.

I'm seeing statements like, "What the hell is a number line and why do kids need it?" Or, "just teach them the basics." The notion of using a manipulative, playing with numbers, breaking them them apart and comparing processes is somehow viewed as non-mathematical.

The truth is that number lines are powerful tools for understanding integers. True, when subtraction is something simple that requires no "borrowing" it feels like a joke. However, the goal is to build up number sense. It's to help them understand math conceptually. If you flip the numbers and end with a negative number as an answer, suddenly a number line helps make the negative-positive relationship more powerful.

This parent's snarky answer about "the process used would get you terminated" is based on a faulty assumption that a first grader needs the same approach as an engineer. And yet . . . this "new math" approach that people mock is something we use constantly in real-world, mental math.

Consider it this way: You have fifty-three dollars and you need to give someone twenty-seven dollars. What are you going to do to figure it out? If you find yourself breaking by tens and going backward, chances are you are using a mental number line.

Oh, you could pull out a piece of paper and do that math that way, but chances is are that as an engineer, you'd be fired . . . or at least laughed at.

I remember someone posting an angry rant about doing multiplication by breaking it up into different pieces. "Just teach the algorithm!" the parent posted.

I posted a response. "If the bill is 27.42 and you want to leave a twenty percent tip, what's the answer? How did you find it?"

Some people divided by five. Others multiplied by .2. Still others moved one decimal over and doubled it. Some rounded up to thirty. In other words, there were multiple processes that worked and each of them involved understanding the properties of numbers. In other words, most people used a process mentally that they were openly mocking on Facebook.

*   *   *

Oddly enough, many of these same people who are mocking "new math" in their posts are also lamenting the fact that Singapore is kicking our butts in math. What they fail to realize is that the places where math is working are the places where they are building number sense.

I've seen what happens when students lack number sense. They learn a lockstep process and think that math is the same as baking a cake. They follow the recipe without understanding why they are doing what they are doing. However, when they get into something as simple as linear equations, they struggle to know what to "do first," when there are often two or three options.

When students lack number sense and they get the wrong answer, they fail to understand why an answer is illogical. You end up with a student who misplaces a decimal number and never finds his or her mistake. Asking students to think conceptually and engage in diagnostic problem-solving isn't superfluous. It's actually part of "the basics."

I know that the "new" math looks different, but instead of criticizing it for being hard or being complicated, try thinking about the theories behind it. There's a reason we're using manipulatives, breaking things apart, using number lines and comparing processes. This is how math works.

Monday, March 17, 2014

Linkfest for Monday, March 17

I still have too many tabs open, but the rest of them are not math...

Friday, March 14, 2014

Calculus: e and pi Are Both Transcendental

Yesterday I was introducing the number e, and telling the students that my preferred definition of e is "the number that makes a slope of 1 for the graph of y=ax at x=0." I also told them that this definition makes mathematicians unhappy, and wrote out the limit definition. But I like them seeing a concrete meaning for this strange number.

As I made this introduction, I mentioned that, like pi, e is irrational (not a ratio of whole numbers) and transcendental (not the solution to an algebra equation using whole numbers). I showed them the proof that the square root of 2 is irrational. But it is the solution to x2=2, so it's an algebraic number, not a transcendental number. I told them that I have not yet completely understood the proof that pi is irrational. (Updated link: Brent Yorgey, one of my favorite bloggers, posted a good series explaining it at The Math Less Traveled. But I never managed to get all the way through it.)  "So it's not really math for me to say pi and e are irrational, when I don't know it by a proof but only by believing what I've been told."

And then I decided that since pi was in the air, and Pi Day was coming, we'd do an activity I'll be doing today with a different group. I had them all stand up around the outer edges of the room, and hold hands, arms outstretched. The extra people made a diameter along the middle of the room. While I was getting them to stretch, I pulled people out by saying "You're out." They laughed. I told them it was a good kind of out, that we were the circle makers.

The reason I'm posting this silly, super simple activity? When we were done, and they counted off, it turned out that there were 22 around and ... (you know I was holding my breath) ...  7 across the middle! I couldn't believe it. I was glowing, further proof to my students that I am a total nerd for math.  ;^)

 In case you're wondering why getting 22 around and 7 across was so special, that makes circumference / diameter = 22/7 = 3.1428, almost perfect. And before calculators made people think decimals were cooler than fractions, 22/7 was the estimate for pi.

(Added on 3/14: Tried it again today in a smaller space. We got 17/4. Bummer.)

Tuesday, March 11, 2014

Join the Math Circle Institue at Notre Dame, July 7 to 11

Math Circle Institute
July 7th – 11th, 2014 

The seventh annual Math Circle Institute will be held on the Campus of Notre Dame, in South Bend, Indiana, from July 7th to 11th, 2014. Both novice and experienced Math Circle leaders are welcome. Bob and Ellen Kaplan, Amanda Serenevy, and Nathan Pflueger will demonstrate the Math Circle approach, and participants will prepare and teach their own Math Circle classes with 1st to 12th grade students who attend each afternoon.

Applications can be made by e-mail to

The institute is wonderful. If you can go, do it. You'll be so glad you did.

[Past blog posts about my experiences there: year three, year five, year six. (I can't believe I never posted about the first two amazing years.) And a post sharing Rodi Steinig's experiences at the Institute, including her great list of quotes from Bob, which became the lovely list now known as Becoming Invisible.]

Here's a repost of what I wrote about it a few years ago...

Bob & Ellen Kaplan (founders of the Boston area math circles, and authors of Out of the Labyrinth: Setting Mathematics Free and many other intriguing math books),  along with Amanda Serenevy (founder of Riverbend Community Math Center), run the fabulous week-long Math Circle Institute, held on the beautiful campus of Notre Dame. This summer is their 7th annual Institute.

For only $850, you get room and board... (The food is amazingly good for such a huge operation - not quite up to my personal organic, local, sustainable standards, but really yummy, with an incredible variety of choices.) ... and then you get to play with math all day. My friend, Ellen H, and I used to call it the math spa. (We went swimming every morning before breakfast.)

The first year I was amazed that I could do math all day long and never get tired of it. There's lots of freedom to explore in whatever way works best for you.

Arrive: Sunday, July 6 (or as early as you can on Monday, July 7). Notre Dame is in South Bend, Indiana, 2 hours from Chicago.

Five days of math circle mania:
  • participate in math circles in the mornings,
  • run one math circle for kids late one afternoon, and watch your colleagues try it out on the other afternoons,
  • discuss the ins and outs of math circles and other fun ways of doing math in the early afternoons,
  • informal math play in the evenings,
  • play with Amanda's collection of math toys and browse her collection of math books, whenever you want,
  • plot, plan, and socialize to your heart's content in between all that.
Depart: Saturday, July 12

Sunday, March 9, 2014

Linkfest for Sunday, March 9

I have to clear out all my open tabs!

I really like Maria Droujkova's response to someone who asked about the Common Core. She (oh so diplomatically) mentioned what she likes. The mathematical practices:
1. Make sense of problems and persevere in solving them.
2. Reason abstractly and quantitatively.
3. Construct viable arguments and critique the reasoning of others.
4. Model with mathematics.
5. Use appropriate tools strategically.
6. Attend to precision.
7. Look for and make use of structure.
8. Look for and express regularity in repeated reasoning.
Although I'm not sure their list is any better than Avery Pickford's Mathematical Habits of Mind. In other words, it's a good list, but not the only good one.

Chain Rule: Experiments, Proof, Practice

Part One: The Plans
Tomorrow I start our third unit in calculus with an introduction to the chain rule. This deep into the semester, I have usually lost most of my creative energy, and don't find time to think this lesson out carefully. I'm teaching great groups of students this semester, which is helping keep my enthusiasm high. So today I'm planning my chain rule lesson.

Describing Composition
First, some functions that we cannot find the derivatives for, because there's more than the variable inside the function. Like y=sin(2x). Here we will review the language of composition.

Experiment by Graphing
Then a graph of the function, to see if we can figure out what the derivative ought to be.

I don't usually write blog posts before I teach the class. This is an interesting point in my process. Where I go next with this may depend somewhat on the students' response to the graph exercise. I know right now that I'm not sure of their response, and that their response may inspire me to move a different direction than what I'm planning right now.

Experiment Algebraically
Where I think I'll go is this. We next take a look at functions which exhibit composition, but don't really have to (ie, they can be simplified). My three examples for now are:
y = (5x-6)2
y = (2x)3
y = √(9x)

I'm going to work through finding the derivative without chain rule, and trying to get the derivative in a form that matches the function. I think this will be another way to experimentally figure out the chain rule. 

Prove It
Then we'll do the proof. I found a much nicer proof here (click on the discussion link) than the one in our textbook (Anton). Except that one vital step seems to be missing. 

Practice It
And after that, we'll do lots of practice. The textbook is probably fine for that, if I can't think up enough examples on my feet.

[I found some inspiring posts, but I'm not sure if or when I can use them: Sam's filing cabinet led me to lots of good posts, one of which was this on the monkey and the mathematician. I might suggest my students check this linked wheels applet out on their own.]

Part Two: How It Went
I got up to the first algebraic example on Monday. On Tuesday, we did the three algebraic examples. They weren't enthusiastic about walking through the proof, so I asked them to look it over on the handout shown below. We finished up by practicing with lots of examples.

Tuesday, March 4, 2014

Linkfest for Tuesday, March 4

So many good posts lately! How will I ever remember all this good stuff?!

Eleven really good ideas in one day?! It's too much!

Monday, March 3, 2014

Linkfest for Monday, March 3

Sunday, March 2, 2014

Please Join: Help the New Math Ed stackexchange Site Become a Reality

Ben said it better than I can:
... based on my experience of the incredible usefulness of the StackExchange sites Math StackExchange and MathOverflow, I think this site could become a great resource.

Another site to follow? Oh my! But if it's a good place to get our math ed questions answered, I'm all for it.

Stackexchange will only start up a new site if 200 people have committed to it. This site is 85% of the way there. (I was number 171.) If you want to help make this site a reality, click here.

Stack Exchange Q&A site proposal: Mathematics Learning, Studying, and Education
Math Blog Directory