
A few days ago I mentioned I was looking for a book of word problems to supplement JellyMan's Saxon Algebra 2 book. Well, I don't know what I was thinking. I have several perfectly good math books just lying around not being any good to anybody, and he can just work the word problems in those. Duh! All I need to do is spend a few hours going through the books and selecting the hardest most suitable problems. I decided to start with Modern Algebra and Trigonometry: Structure and Method Book 2 because that's the book my dad tortured me with when I was a kid. There's a relationship there.
As I was flipping through and circling the hardest most suitable problems, I found a section about finding the greatest common factor of two numbers using the Euclidean Algorithm, and I thought, "Cool! The Goobs totally need to see this." So I copied the section, pretty much word for word, onto the white board and waited for The Goobs to wake up.
They must have heard my earnest scribblings in their sleep, because I waited a long time. When they finally came downstairs, this is what they saw (click to enlarge):

They threw up their hands and hissed and writhed in the sunlight. It wasn't pretty. So I fed them their breakfast and started over from the beginning, and I'm going to share how I taught this concept just so you can fully appreciate why I generally leave the math instruction to the good people who wrote our textbooks. (Psssst - it's because I'm a really crappy math teacher.)
"Okay, Goobs. Who knows the greatest common factor of 1149 and 460? Anyone? Anyone? Okay, I don't know either. Just ignore that Euclidean Algorithm bit at the top, and I'll show you how to do it:"

"When you get to a remainder of zero, that divisor is the G.C.F. Got it? Good. Try with, let's say, 897 and 143. (waiting, waiting, waiting) Okay, good. You got it. Is anyone interested in why this works? Anyone? Anyone? Well, you're going to learn why anyway. Deal with it."
"Aw, Mom! It's the weekend! I hate math! It makes my brain shrivel! Aaaagggh!"
"Shut up and pay attention, darlin', you're making my eyes bleed. Okay. When we write 'each of the four steps in the form:

"you can see that 23 is a divisor of each divisor and also of each remainder. It must, therefore, be a divisor of each dividend, and the G.C.F. of 460 and 1449 is the same as that of 46 and 23, namely, 23.' I can't help it, sweetie, that's what the book says. I'm reading word for word. I'll read it again . . . here, you follow along . . . do you understand now? Really? Tell me."
"23 will go into everything you divide by and everything left over, so it's the greatest common factor."
"Okay, good. Now listen to this:"

"Remember, any time you see 'in general' written in a math book, it means 'not always, but close enough that you won't have to worry about it, at least in this chapter.' Do you both understand what's on the white board? Anyone? Anyone?"
*crickets*
"Okay, how about if I show you how all these a's and b's and symbols relate to the original problem..."

"Better? Okay, good. Now, listen up. 'Successive division produces the sequence of equalities:'"

"'Since the successive remainders are decreasing nonnegative integers, you must ultimately arrive at a 0 remainder. The G.C.F. of a and b is the last positive remainder in this sequence.' Got it?"
*crickets*
"Okay, let's plug the values of the original problem into these equations so you can see it more clearly. JellyMan, what does a equal? Good. Anemone, what is b? Good. Now, q1 is... the first quotient, that's right, so r1 has to be... yes, the first remainder. And so on. What would the next thingy - I mean, term, no, I mean equality - in the sequence be for our problem? Good."

"' The process of obtaining a G.C.F. in this way is attributed to Euclid - yes, JellyMan, the geometry guy - and is referred to as the Euclidean Algorithm.' Isn't that cool? What? Oh. Sure, you can go play Wii."
At least I've got the crickets to keep me company. *sniff* My dad will be so proud.