# "how to" videos by Dave HaxNovember 11, 2014 3:00 PM   Subscribe

I have to go fold shirts now.
posted by frykitty at 3:14 PM on November 11, 2014 [6 favorites]

This man needs to be President or Prime Minister, or Dictator, or Army General (depending on your local Government circumstances)
posted by greenhornet at 3:19 PM on November 11, 2014

Holy shit the multiplication thing.
posted by Mister Moofoo at 3:27 PM on November 11, 2014 [4 favorites]

Before you get too excited about the multiplication with lines thing, try it with numbers that use larger digits. There's a reason they always demonstrate with things like 13 x 21. Draw out something like 76 x 98 with lines, and see if you still feel it's any easier.
posted by evilangela at 3:33 PM on November 11, 2014 [10 favorites]

The multiplication thing looked pretty tedious, but doable for someone with dyscalculia. Multiplying makes me cry, but I think I could handle this until I got to larger numbers and had to carry over.
posted by frykitty at 3:37 PM on November 11, 2014 [1 favorite]

Love to see multiplication of two seven digit numbers. For more than two numbers just draw the lines in extra dimensions?
posted by sammyo at 3:38 PM on November 11, 2014 [4 favorites]

I could see where he kept the digits between 1 and 4, but figured that's for ease of teaching and brevity of video.
It's still nifty, and not a thing I'll need to do much, what with always having a calculator now.
But I wish I had learned that in school instead of memorizing a table.
posted by Mister Moofoo at 3:42 PM on November 11, 2014 [1 favorite]

The Mango peeling technique may change my life if I can get it to work. I'd bee thinking about "inventing" a "sharp spoon" but, gotta try this.
posted by sammyo at 3:47 PM on November 11, 2014

Meh. I prefer Alantutorial.
posted by grumpybear69 at 4:28 PM on November 11, 2014 [3 favorites]

And after watching the shirt folding video I retract my statement. This guy is awesome. Please note that, for the,shirt thing to work, you need to pinch again at point C.
posted by grumpybear69 at 4:37 PM on November 11, 2014

My dad taught me the circle thing 45 years ago.
posted by Uncle Grumpy at 4:38 PM on November 11, 2014

This is cool, but I am still a bit disappointed that it doesn't show how to draw a perfect freehand circle the way my math teacher could in college – on a chalkboard, in one motion.
posted by koeselitz at 4:39 PM on November 11, 2014 [5 favorites]

The lines thing helps exactly nobody. If you have more digits or even just less fortuitously-chosen double digits, you are going to have problems. It certainly won't help someone with dyscalculia, unless that means "can count, add and carry with easy, but cannot memorize the one-digit multiplication table".

13x21 is super easy anyway.

13x21 = 13x20 + 13 = 13x10 + 13x10 + 13 = 130 + 130 + 13 = 260 + 13 = 273.
posted by DU at 4:53 PM on November 11, 2014 [2 favorites]

Freehand the was killed off by Adobe, so I don't know what he's talking about.
posted by Brandon Blatcher at 4:54 PM on November 11, 2014

13x21 is super easy anyway.

13x21 = 13x20 + 13 =....

You, sir, are very funny!
posted by rtha at 5:03 PM on November 11, 2014 [1 favorite]

13*21 13*7 91*3 273
posted by Oyéah at 5:04 PM on November 11, 2014

Not understanding that 13 x 21 = 13 x 20 + 13 is indicative of a grasp of math equivalent to being able to read up to "See Dick run" and no farther.

13 x 21 means that you have twenty-one 13s (or thirteen 21s).

Twenty-one 13s is twenty 13s + one 13.
posted by DU at 5:06 PM on November 11, 2014 [4 favorites]

Not understanding that there are a variety of reasons why "it's so easy!" might not apply to everyone - including otherwise decently educated and smart people (and being insulting when pointing it out, to boot) is indicative that one may be ignorant about how people's brains work!

This is fun!
posted by rtha at 5:15 PM on November 11, 2014 [8 favorites]

Neat, but pretty much the opposite of freehand... fixed hand maybe?

(edit) Even better: flesh compass.
posted by grog at 5:18 PM on November 11, 2014 [1 favorite]

13 x 21
Thirteen times twenty-one. Break it down:

1 x 2 = 2
One times two is two!

1+ 3 + 2 + 1 = 7
Add all the digits and they equal seven!

3 > 2 > 1
Pick the biggest digit - three!

273
Two seven three is the answer!

I hope this helped.
posted by Joe in Australia at 5:29 PM on November 11, 2014 [10 favorites]

13x21 is super easy anyway.

=[r1(cosθ1+i⋅sinθ1)]⋅[r2(cosθ2+i⋅sinθ2)]=r1⋅r2[cos(θ1+θ2)+i⋅sin(θ1+θ2)] = potato
posted by greenhornet at 6:00 PM on November 11, 2014 [4 favorites]

"lol math is hard" is pretty tired. Unless you have an actual brain dysfunction, there is absolutely no reason you can't understand 21 = 20 + 1. It's literally 3rd grade math. Imagine someone said to you that their brain just couldn't get the difference between verbs and nouns. Yeah, that could be, if there was a damage issue. Otherwise we are talking about cultural "wisdom" you just need to overcome.
posted by DU at 6:13 PM on November 11, 2014

It's interesting seeing how many different ways we all use to reach 273.

For me it is 13x21 or:

10x21=210 then 3x21=63 added to 210 = 273.
posted by notreally at 6:14 PM on November 11, 2014 [1 favorite]

I actually would not have done it the way I said. 13x21 = 10*21 + 3*21 = 210 + 63 is a lot easier.

It would be even cooler, but far less obvious, to do (17-4)(17+4) = 17^2 + 4^2, but you'd have to have 17^2 memorized, which I don't.
posted by DU at 6:19 PM on November 11, 2014

My brain would have done 13X2 = 26, X10=260, +13 = 273.
posted by Hazelsmrf at 6:21 PM on November 11, 2014 [2 favorites]

there is absolutely no reason you can't understand 21 = 20 + 1

I think you must have never attempted to teach anybody anything. It's not misunderstanding that 21 = 20 + 1. It's not having the practice to think of 13 x 21 = 13 x 20 + 13 being the first step of one method of solving the problem.
posted by transient at 6:26 PM on November 11, 2014 [1 favorite]

I have taught my kids (and others) this same method when they are in like kindergarten, much harder things later. If you teach them before the "my brain hurts!!11 lol" crowd indoctrinate them they have absolutely no difficulty.
posted by DU at 6:30 PM on November 11, 2014 [1 favorite]

Absolutely no one is saying "lol my brain hurts" here, but people's brains work differently. Some people are more visual. When I teach things I try to think of at least three different ways to explain it to different learners. And hey, some people just don't have to work with math very much and have been out of practice looking at equations for decades. They might find this useful. The lines thing doesn't work for you; cool. No need to be dismissive of the way other people learn.
posted by transient at 6:42 PM on November 11, 2014 [1 favorite]

25 / 5 = 14
posted by Wet Spot at 6:46 PM on November 11, 2014

I'm confused about all the "but he used easy examples" for multiplication complaints. He finishes the video using (1) examples involving carrying---which were really nice, because you're moving (carrying!) the extra digits over to the next place value---and (2) multiplying 3 digit numbers (ok, 3 digit by 2 digit, but it's clear how the method generalizes).

His examples wouldn't've been better if he'd used 768x984 or something, there would've just been a lot more dot counting. But all the methods were clear, I thought.
posted by leahwrenn at 7:13 PM on November 11, 2014

All I know is I'm gonna make an office supply crossbow tomorrow and run around my workplace like a crazed Ted Nugent.
posted by rocket88 at 7:33 PM on November 11, 2014 [4 favorites]

What I like about the lines multiplication trick is that it helps with understanding the combinatorial nature of multiplication - as you draw the lines you can intuit the relationship between lines and crossings and how that relates to what multiplication actually is.

Unlike many tricks (and most standard methods) which are pure process with little to no insight to the mathematical object they operate on.
posted by idiopath at 7:42 PM on November 11, 2014 [2 favorites]

don't preserve your garlic that way you will die of botulism.
posted by Mei's lost sandal at 8:04 PM on November 11, 2014 [1 favorite]

The multiplication trick is cute but it seems cumbersome compared to just, you know, multiplying the numbers. But as has been said, it's great to teach using a bunch of techniques because each person learns differently and for someone this is going to be revelatory.
posted by Dip Flash at 8:55 PM on November 11, 2014 [2 favorites]

The perfect circle video is disappointing; it's not really freehand, you're keeping your hand still and using it like a compass. Why not just use a compass? Why not trace a jar lid? Where is the artistry? Where is the skill? Why i am i SO ANGRY ABOUT THIS
posted by Greg Nog at 9:04 PM on November 11, 2014 [2 favorites]

Sounds like you need to make a mini bow & arrow and light the tiny arrow on fire. Did I forget to mention you can light the tiny arrow on fire? I think you will find it soothing
posted by flex at 9:07 PM on November 11, 2014

DU: "The lines thing helps exactly nobody. If you have more digits or even just less fortuitously-chosen double digits, you are going to have problems. It certainly won't help someone with dyscalculia, unless that means "can count, add and carry with easy, but cannot memorize the one-digit multiplication table".

13x21 is super easy anyway.

13x21 = 13x20 + 13 = 13x10 + 13x10 + 13 = 130 + 130 + 13 = 260 + 13 = 273.
"

I mostly agree, but it is an interesting visualization of the normal multiplication method.
posted by pwnguin at 9:25 PM on November 11, 2014 [1 favorite]

I learned the freehand circle trick from Seb Lester's gorgeous calligraphy channel just two weeks ago!

Greg Nog: Because it doesn't poke holes in the paper, and you might not have a jar lid of the right size, and you can do this with whatever pen or brush or other instrument you want to use?

Also, the description for the multiplication with lines video calls it a "Japanese multiplication maths trick", which immediately sets off my orientalism warning bells. Sure enough:
"Is there something similar for division as this Japanese multiplication method? [. . .] I'm hoping someone from the Japanese schooling system might know since this seems to be primary school stuff there."

"I've been living in Japan for 15 years. In fact, that method is called "Indian multiplication method" in Japan. Though I don't know whether or not it actually came from India, many people believe so because they usually regard Indians as mathematically talented people. This method is not so common in Japan, yet some cramming schools teach this method for elementary school students."

"Wow...that's interesting. No, I haven't heard of any schools in India ever teach this. I'm Indian."
posted by narain at 9:25 PM on November 11, 2014 [2 favorites]

there would've just been a lot more dot counting

Um, yeah. Like counting hundreds and hundreds of dots. It's not easier that way. And in fact it's not even different. You're counting the dots in a times grid, just like your "old-fashioned" multiplication tables. All of the multiplication methods are essentially the same thing. You're confusing notation with mathematics, as Vi Hart beautifully explains, and demonstrates, in Latius's link above.
posted by Fnarf at 10:13 PM on November 11, 2014 [1 favorite]

I think tricks like the multiplication thing are important to teach and to learn, for kids like I was, because I had such an awful time with math in grade school.

I didn't realize until I was in my mid-twenties why this was, since I enjoyed learning, and got a lot out of reading all the little sidebar exploration things in the textbook that we never covered in class. Like the so obvious thing about multiplication being repeated addition: Never stated out loud.

But before I hit multiplication, the damage was done. What I finally figured out was this: I learned the single-digit addition problems, aka "math facts", by learning the sounds of the words together, as much as or more than the actual combination of values. "Five and two is seven" or "six and three is nine" became bits of verbal music, little pieces of poetry, which felt comfortable in my head, just like "Jack and Jill went up the hill" or "Mary had a little lamb", et cetera.

Which is fine for addition, but "minus" was so much less musical for me, and I was soooooo sloooooow at subtraction, because I didn't burn subtraction poems into my head, because "minus" is an ugly-sounding word, and not conducive to making these things stick in my widdle head, so then I had to do the actual math, which I had cheated myself out of doing, and I was damn sure not going to count on my fingers, which A) was "for babies" (or so the teachers would say) and B) I hadn't ever been taught how to do, anyway (even at that young age, I thought most things people did had specific and proper methods, and if I wasn't taught the steps, I was afraid to do it. That my method for addition lined up with the right way most of the time obscured the fact that my method was faulty.).

So for a few years, I struggled really hard with subtraction, and then multiplication came along, and while I was interested in learning the process via some method of repeated addition, I was expressly forbidden to write, say, 8+8+8+8+8+8 on my paper, and taught to multiply by memorizing the tooth-grating "times tables" (can I tell you how I screamed inside when kids [or even teachers!] would say "times it by 4"?) which give you the data in a non-useful way, by dumping a bucket of content on you and hoping some of it sticks, rather than teaching a useful process you can put to work discovering the answers rather than relying on memory, or on having a machine do the work for you.

I still struggle with math, and I really do blame the way it was taught, at least as much as my own admitted laziness. I'd probably have been less lazy about it if I had been shown a different (fun!) way of doing it.

Let's not even get into the fact that nobody ever spoke of short division, which next to the nightmarish guessing-game of long division, seemed like some kind of proof of the existence of Santa Claus when I finally found out about it, when I was in my thirties.

Okay. Math rant over.
posted by Mister Moofoo at 10:13 PM on November 11, 2014 [6 favorites]

I'm still not really sure about the difference between short and long division. I think I wasn't paying attention in class or something, and I just used my own techniques. I still do, but I feel kinda bad about it.
posted by Joe in Australia at 12:31 AM on November 12, 2014

Short division doesn't climb down the page, eating up precious notebook paper, and it also makes it easier to do something with those irritating remainders.
posted by Mister Moofoo at 12:42 AM on November 12, 2014

I'm intrigued that this thread has gone for the "how to multiply" discussion, and not the "how to make a crossbow out of pencils and rubber bands that SHOOTS FLAMING ARROWS" discussion. "You should only do this outside, somewhere safe where nothing can catch on fire," he says in the bow and arrow video, over a shot of one fired indoors at plastic toys...

As for his flaming pumpkin, it makes my efforts with tea candles look positively feeble.
posted by rory at 3:45 AM on November 12, 2014

All I know is I'm gonna make an office supply crossbow tomorrow and run around my workplace like a crazed Ted Nugent.

In other words, Ted Nugent
posted by Ray Walston, Luck Dragon at 4:41 AM on November 12, 2014 [1 favorite]

How to Pack for 1 Night and How to Pack a Suitcase Efficiently are ingenious.
posted by rory at 4:43 AM on November 12, 2014

How to pack is interesting, but doesn't address the carry on suitcase is too damn small for 14 days worth of winter clothes that I have vs purchasing expensive dual use stuff I can't afford anyway after purchasing the overpriced plane ticket, and I need something dressy as well as something to hang out at the barn problem.
(Suitcase resembles this sentence)
posted by BlueHorse at 1:36 PM on November 12, 2014

Crazy Russian Hacker
posted by ivandnav at 3:24 PM on November 12, 2014

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