Observations on the PARCC sample Algebra II exam

Fresh off the presses at

http://practice.parcc.testnav.com/

you can now find complete PARCC sample exams. Since it’s the one I most likely have to worry about next year, I tried out the Algebra II exam.

While I haven’t checked the other tests yet, the Algebra II has laid off the “show your work” type question. I’m going to put this in the positive column (I was deeply worried about open responses being graded by an army of interns; plus the turnaround needs to be very fast because this is technically the final for our Algebra II class. Imagine having to shave off an extra two months from the end to give time for the test to be graded). [ADD: According to this comment, this only applies to the final exam, and there are still “show your work” type questions on the other tests.]

Some question-by-question comments:

parccsample1

I admit I was baffled enough by this one to check Wolfram Alpha (I got m = -15/2 where m = 1 was extraneous), until I realized the key phrase “you may not need to use all of the answer boxes”. We’re going to have to specially train students for that trick, I think.

parccsample3

I tested this one on my students. The majority put the value for x which makes the statement true (1) not the extraneous solution (-3/4). I can understand the motivation here: forcing students to go through the factoring rather than just test numbers or even eyeball the thing, but putting the extraneous solution as an answer is rare and I can imagine a legion of students being confused by this.

parccsample2

I always considered the trick of rejiggering a number’s base (turning 4 into 2^2) to be something of a side trick; I’ve never had to use it outside a college algebra book.

parccsample4

Because saying “complete the square” would be too easy. In all seriousness, this is one of those problems I would have many students know how to do but get intimidated by the language of the question.

parccsample5

So the first 8 questions (which I was just quoting from) are in the non-calculator portion of the test. The remaining 26 are from the calculator portion. The students will have access to a TI-84 emulator.

parccsample6

I’ve got mixed feelings on this one. In a way it’s a neat bit of factoring (yank out the (x-y) terms, and what remains will be a difference of squares, tossing an extra (x-y) on the pile) but it also looks nothing like the kind of factoring from any textbook I’ve used; I’m fairly sure our Carnegie Learning book (which was written from scratch specifically for Common Core) has nothing like it.

parccsample8

The number of fancy widgets to enter answers has dropped considerably, but here’s one; you drag and drop in order.

Also noteworthy: there are two problems involving average rate of change. I think in our textbook there was enough material to squeeze out a single day. The PARCC writers must be putting rather more emphasis on it.

parccsample9

Here’s another widget: the dots are dragged around to form the graph. I was somewhat thrown by the dots not just snapping to the grid but also the halfway points. I believe this is a bad idea. A student could easily think they have a correct answer but leave the dot halfway rather than right on the appropriate point.

parccsample10

My students would be thrown off by the wording here. I think the intermediate step is actually helpful, but the phrase “Product of greatest common factor and binomial” looks so technical many of them would shut down.

parccsample11

I’m used to tests that make the statistics so easy students can answer them with no training whatsoever, but this is what I’d call a real statistics question.

parccsample12

This is a widget that lets you select an interval on the number line. In the process of trying to enter an answer the number line disappeared. Then going back a question and returning I was unable to get anything to appear at all.

Mathematics classes do not teach mathematics literacy

Both the phrases “mathematics classes” and “mathematics literacy” can be ambiguous, so I am meaning–

“Mathematics classes”: The high school curriculum delivered to a typical student in the United States. This usually excludes classes like “Statistics” or “Financial Math”.

“Mathematics literacy”: The kind of “good citizen” math that people refer to in articles like Headlines from a Mathematically Literate World. The word can also mean “ability to problem solve”, but that’s not what I mean here.

Taking the Headlines article and the classes of a typical high school mathematics student, how many of the headlines would a a student understand?

At the very least, understanding the entire list requires knowing about: correlation vs. causation, inflation, experimental replication, estimation of large numbers, incompatibility of comparisons with different conditions, understanding how tax brackets work, meaninglessness of predictions within a margin of error, statistically unlikely events, and reversion to the mean.

None of these will ever occur in an traditional math class. In other words, in the list of supposed math literacies, the typical math student in the US receives zero of them. (Some might possibly show up in a class labelled “Economics” or “Free Enterprise”, but those don’t get called Math Classes).

It’d be fair to argue I’m being highly specific in my starting definitions, but I often see the “good citizen” argument used during a general “why are we teaching math” type discussion which assumes a traditional math class track. That sort of argument only works if people are prepared to also overhaul the curriculum (by putting, for example, statistics before calculus as Arthur Benjamin discusses at TED).

Why is a negative divided by a negative a positive?

So there’s a whole lot of posts, including one from this very blog, which give intuitive explanations of why a negative times a negative is a positive.

plusminuslarge

I haven’t seen nearly as much material for a negative divided by a negative. One can certainly appeal to the inverse — since 1 \times -1 = -1, \frac{-1}{-1} = 1. Google searching leads to answers like that, but I’ve found nothing like the multiplication picture above.

Can anyone explain directly, at an intuitive level, why a negative divided by a negative is a positive? Or is the only way to do it to refer to multiplication?

The evolution of mathematical exposition

More rambly and unsubstantiated than usual, apologies —

early19thsample

[Source.]

Theory: Mathematical exposition has evolved just like fiction writing has. However, tradition has held stronger in mathematics (likely due to a need for precision) and it means that clarity in writing is if not actively discouraged at least passively devalued.

Theory: We are not anywhere near the threshold of simplest and clearest explanations in the exposition of mathematical subjects.

Still, what used to be difficult is now considered easier. Various subjects have shifted their supposed level. For instance, not long ago College Algebra was the prestige class at the top of the high school level.

Furthermore, our raw definitions of what each class is has shuffled the actual content of subjects; Algebra I from the 1940s is not the Algebra I of today.

Theory: It would be possible to take a “hard” subject like group theory or transcendental number theory and make it comprehensible at a lower level. However, as there is no requirement to do so there is little motivation to make the subject easier. When a curriculum shift happens to move topics to a lower level, mathematical exposition evolves to catch up.

Book update (and call for testers)

Don’t get too excited yet — the big one (Why Algebra Works, you’re best off reading this post for an idea of how it is being written) isn’t done.

However, in the midst of work I realized I was assuming the readers would remember how integer operations went, and it was quite possible they forgot, so I worked on a appendix. The appendix ballooned into a full fledged … short story? novella? … and got to the point that I even separated addition/subtraction from multiplication/division.

So the first part (addition/subtraction of integers) is close to ready, and it does follow my percepts, namely–

1.) that it should have a smooth writing style modeled after popular math articles (like Steven Strogatz or Martin Gardner) rather than textbooks

2.) that there are no “problems” but rather “puzzles”, roughly defined as anything that wouldn’t be out of place alongside a Sudoku book or in the middle of a Professor Layton game

3.) that there is a strong emphasis on meta-thinking; that is, having readers examine whatever mental model they are using in a particular part of mathematics and diagnosing where misconceptions may come about at the internal level.

As an example of #3, I start by asking the reader to add 2 + 2 (really), examining the possible ways of visualizing it and which ways might be more or less helpful.

In any case, everything is so unlike the textbook approach that I need some beta testers. In particular, while I would like some people who are adept in mathematics, I would also like some people who think that are not good at math or even actively dislike it. I’m guessing the latter don’t read this blog I’m going to need some help — if you know someone who might be a good candidate, could you send the word along? I’ll get back to everyone in a few weeks.

You can either post here or toss a line to my email over at my About Page.

Impossible Learning: watch someone trying to learn calculus from scratch

David Wees retweeted this from Jared Cosulich:

It turns out Impossible Learning is a just-started-last-month blog where Jared is trying to learn Calculus and post about his struggles. It’s terrific and you should read it. See him ask the perennial question When Will I Use This?

And I immediately found myself saying “come on, when am I ever going to have to find the limit of this random equation”.

I felt like I was back in High School again.

But seriously, why is this one of the first things I’m directed to learn when I want to know more about Calculus? Why is it so hard for me to find some practical applications of this material? I know there is value in understanding the abstract math, but I’d like to balance that with at least some understanding of how this works practically…

Or his attempt at explaining the power rule:

I don’t think this actually counts as a proof, but it definitely made the “Power Rule” click for me a bit more. Basically it’s saying that the derivative of a square (x²) is two lines (2x) and the derivative of a cube (x³) is three squares (3x²).

So for a square to get a tiny bit bigger you need to add on two lines (one to the top and one to a side). Similarly for a cube to get a tiny bit bigger you need to add a square to three sides (e.g. top, right, and front).

Counting puzzle from the first US puzzle championship

My students had fun with this one today. Part d is what showed up in the actual championship.

One night, in an attempt to combat insomnia, you begin counting (1, 2, 3, …), but you decide to do it digit by digit. As you go along, for example, the 15th digit you count is the 2 of the number 12.
1 2 3 4 5 6 7 8 9 10 11 12

a.) What’s the 50th digit you count?
b.) What’s the 100th digit you count?
c.) What’s the 1000th digit you count?
d.) What’s the 1,000,000th digit you count?

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