Showing posts with label math. Show all posts
Showing posts with label math. Show all posts

Tuesday, August 1, 2023

A Better Way to Think about %

A lot of people get confused by the "%" symbol. I can understand why. Even https://en.wikipedia.org/wiki/Percentage seems way more confusing than it should be.

Well, maybe I can help. 

Here's a simplifying little idea that I learned by reading ISO 80000-1: 

The percent symbol (%) is just a constant, just like π or e. Its value is 0.01 (or 1/100, if you prefer).

Let me show it to you in a table. Maybe that'll clear it up:

SymbolValue
π≈ 3.14159
e≈ 2.71828
%= 0.01

What this means is that anywhere you see the "%" symbol, you're free to substitute the value 0.01 if you want:

50% = 50(0.01) = 0.5

So, how does that help? Well, it gives you a simple rule you can apply instead of having to intuit how to convert something to or from a percentage. 

For example, I used to find myself wondering, "If I want to convert this percentage to a real number, do I multiply by 100? Or divide?" I hate memorizing crap like that.

But knowing that % = 0.01 makes it easy. For example, converting 42% to a number without the % sign, I simply substitute, like this:

42% = 42(0.01) = 0.42

When you know that % = 0.01, it's easy to see that 100% is just another way of expressing the number 1:

100% = 100(0.01) = 1

Converting a number to a percentage is easy, too. 

I can of course multiply anything I want by 100% and still have the same quantity I started with. Here's how to convert 0.0005 to a percentage:

0.0005 = 0.0005 × 1

= 0.0005 × 100%

= (0.0005 × 100)%

= 0.05% 

Yep, ISO 80000-1... I don't do everything it says, but this percentage thing was a nice revelation.

Friday, January 14, 2011

An Axiomatic Approach to Algebra and Other Aspects of Life

Not many days pass that I don’t think a time or two about James R. Harkey. Mr. Harkey was my high school mathematics teacher. He taught me algebra, geometry, analytic geometry, trigonometry, and calculus. What I learned from Mr. Harkey influences—to this day—how I write, how I teach, how I plead a case, how I troubleshoot, .... These are the skills I’ve used to earn everything I own.

Prior to Mr. Harkey’s algebra class, algebra for me just was a morass of tricks to memorize: “Take the constant to the other side...”; “Cancel the common factors...”; “Flip the fraction and multiply...” I could practice for a while and then solve problems just like the ones I had been practicing, by applying memorized transformations to superficial patterns that I recognized, but I didn’t understand what I had been taught to do. Without continual practice, the rules I had memorized would evaporate, and then once more I’d be able to solve only those problems for which I could intuit the answer: “7x + 6 = 20” would have been easy, but “7/x – 6 = 20” would have stumped me. This made, for example, studying for final exams quite difficult.

On the first day of Mr. Harkey’s class, he gave us his rules. First, his strict rules of conduct in the classroom lived up to his quite sinister reputation, which was important. Our studies began with a single 8.5" × 14" sheet of paper that apparently he asked us to label “Properties A” (because that’s what I wrote in the upper right-hand corner; and yes, I still have it). He told us that we could consult this sheet of paper on every homework assignment and every exam he’d give. And here’s how we were to use it: every problem would be executed one step at a time; every step would be written down; and beside every step we would write the name of the rule from Properties A that we invoked to perform that step.

You can still hear us now: Holy cow, that’s going to be a lot of extra work.

Well, that’s how it was going to be. Here’s what each homework and test problem had to look like:


The first few days of class, we spent time reviewing every single item on Properties A. Mr. Harkey made sure we all agreed that each axiom and property was true before we moved on to the real work. He was filling our toolbox.

And then we worked problem after problem after problem.

Throughout the year, we did get to shift gears a few times. Not every ax + b = c problem required fourteen steps all year long. After some sequence of accomplishments (I don’t remember what it was—maybe some set number of ‘A’ grades on homework?), I remember being allowed to write the number of the rule instead of the whole name. (When did you first learn about foreign keys? ☺) Some accomplishments after that, we’d be allowed to combine steps like 3, 4 and 5 into one. But we had to demonstrate a pattern of consistent mastery to earn a privilege like that.

Mr. Harkey taught algebra as most teachers teach geometry or predicate logic. Every problem was a proof, documented one logical step at a time. In Mr. Harkey’s algebra class, your “answer” to a homework problem or test question wasn’t the number that x equals, it was the whole proof of how you arrived at the value of x in your answer. Mr. Harkey wasn’t interested in grading your answers. He was going to grade how you got your answers.

The result? After a whole semester of this, I understood algebra, and I mean thoroughly. You couldn’t make a good grade in Mr. Harkey’s algebra class without creating an intimate comprehension of why algebra works the way it does. Learning that way supplies you for a whole lifetime: I still understand it. I can make dimensioned drawings of the things I’m going to build in my shop. I can calculate the tax implications of my business decisions. I can predict the response time behavior of computer software. I can even help my children with their algebra. Nothing about algebra scares me, because I still understand all the rules.

When I help my boys with their homework, I make them use Mr. Harkey’s axiomatic approach with my own Properties A that I made for them. (I rearranged Mr. Harkey’s rules to better illuminate the symmetries among them. If Mr. Harkey had been handy with the laptop computer, which didn’t exist when I was in school, I imagine he’d have done the same thing.)

Invariably, when my one of boys misses a math problem, it’s for the same stupid reason that I make mistakes in my shop or at work. It’s because he’s tried to do steps in his head instead of writing them all down, and of course he’s accidentally integrated an assumption into his work that’s not true. When you don’t have a neat and orderly audit trail to debug, the only way you can fix your work is to start over, which takes more time (which itself increases frustration levels and degrades learning) and which bypasses perhaps the most important technical skill in all of Life today: the ability to troubleshoot.
Theory: Redoing an n-step math problem instead of learning how to propagate a correction to an error made in step n – k through step n is how we get to a society in which our support analysts know only two solutions to any problem: (a) reboot, and (b) reinstall.
It’s difficult to teach people the value of mastering the basics. It’s difficult enough with children, and it’s even worse with adults, but great teachers and great coaches understand how important it is. I’m grateful to have met my share, and I love meeting new ones. Actually, I believe my 11-year old son has a baseball practice with one tomorrow. We’ll have to check his blog in about 30 years.

Friday, February 27, 2009

Dad, do I really need math?

My kids are pretty good about their math homework. They seem to enjoy it for the most part. It wasn't always that way. When the going gets tough, the natural human response, it seems, is to quit. So at times in our kids' school careers, their Mom and I have had to hang tough with them to try to make them do their homework. (The credit here belongs to their Mom.)

I remember when I was in school, the prevailing attitude in the classroom was, "When are we ever going to need to know this?" The much sadder one was, "My Mom and Dad said that I'm never going to need to know this stuff."

I couldn't have told you, when I was 10 years old, that I'd need to understand queueing theory one day in order to finish an Oracle project I had to do for Fidelity Investments. Or that I'd be able to win a Jim Sundberg autographed World Series baseball by using the distributive law of multiplication in my head while he was showing 400 people how Gaylord Perry liked his signs on the mound. It didn't matter to me, because I just had faith that there was a good reason I was supposed to learn everything I could in school. Having that particular faith was no accident.

I don't remember my Mom and Dad ever forcing me into doing math. I knew, of course, that it was My Job to do as well as I could in school ('A's are loafing unless they're '100's). But I don't remember ever feeling forced.

One of the things I fondly remember my Dad doing with me was glide slope calculation. Dad flew for many years for United Airlines. He retired as a 767 captain a long time ago. One of his priorities as a professional was to conserve fuel for his employer. It used to bug him when a pilot would constantly monkey around with the throttle during the approach to a landing. My Dad told me his goal on approach was to dial back the power one time at cruise altitude, at the very beginning of the descent, and then never touch it again until he turned on the thrust reversers after touchdown.

So he played this game with me, especially on car rides, because it was a 30-minute drive each day to where I went to grade school. He'd give me the altitude we were at and the altitude we needed to descend to, and either a time limit or the number of miles outbound we were. Then he'd ask me to calculate the sink rate in my head. He put triangles into my brain that I could see every time he asked me a question like that, and I'd hatch on it with him until we came up with the right sink rate. Or he would ask me things like, if the nose is pointing to heading 026, then what heading is our tail pointed at. So he put circles into my brain, too.

Every once in a while—oh, and I loved this—he would give me a paper flight plan form, with dozens of tiny cells to fill in, and I would fill them all in. I was 6 or 7 when we was doing that. I of course didn't know how to do it correctly, but I filled it all in anyway. Whenever I was really worried about doing it "right," I'd ask my Dad, and he'd tell me the kinds of things I should write down and which cells I should write them in.

You know the biggest value of that flight planning experience? It was that I couldn't wait to find out in school someday what point meant. You know, as in "three point five." I remember the day in class when a teacher finally taught us about decimal points. I felt sooo cool because now I knew what "three point five" actually meant.

My Dad did things with me that got me interested and excited about doing math, all on my own, without making me feel like I was being punished by it. Thus the abundance of wonderful opportunities that I have today are largely a continuing gift from him. I hope that another gift he gave me is the ability to be a good enough dad myself for my own kiddos, but of course I worry that I'm not doing it enough, or well enough. Telling stories about it helps remind me how important it is.

What reminded me of all this is a little document called "A Short Course in Human Relations," autographed by Bobby Bragan. It sits here in the foyer of our Method R office. I see it every single time I walk through our door. You've probably heard the following statement:
Say you were standing with one foot in the oven and one foot in an ice bucket. According to the percentage people, you should be perfectly comfortable.
Bobby Bragan said that; I think it was in 1963. It is a classic illustration of skew, which is vitally important to my career. Bobby Bragan, though, is an American hero for lots of good reasons. You should read about him.

Well, one night a few years ago, I got to watch Bobby Bragan speak to a small group. His talk was fascinating. He brought a huge box of stuff up to the podium with him, and he warmed up with a game. He opened by pulling something out of the box and saying whoever can answer this riddle gets the prize. The first one was something like, "What has eighteen legs and two breasts?" Shocker, right? The answer was The Supreme Court. Whoever said that, Bobby Bragan tossed him the first prize of the night.

Pretty deep into his speech, he must have given out twenty prizes to people. Not me. I either didn't know the answer, or I didn't say it loud enough or fast enough. I watched prize after prize go out, until he brought out this autographed document called "A Short Course in Human Relations." He read it aloud. It was an important part of his speech. And then he asked the question that went with it: "Nine ballplayers come out of the dugout before each game, and each ballplayer shakes the hand of every teammate. How many handshakes is that?" The voice that said "thirty-six" was mine. I was doggone lucky that Bobby Bragan had asked a bunch of baseball players a math question, and right on the prize that I really wanted, too.

Math. You really never know when you're going to need it.