jail:
this is fucked up. this fucked me up. the teachers fucked up by not showing us this fuck up. fuck.
dear god
i’m 28 and never knew this
WITCHCRAFT
i dont get this
OKAY.
For anyone who doesn’t get this, let me introduce you to something called the Lattice Method, which is basically this, just simplified a little so that it’s easier to manage once your numbers get bigger than, like, sixty. You might have learned about it in elementary school, because it's SUPER SIMPLE and easy to manage, but you almost certainly don’t remember it because your teachers told you not to use it in lieu of long multiplication, which takes a lot more time and has a lot more opportunities to fuck up. The basic idea of the Lattice Method is that you never multiply a number bigger than nine (because who the fuck really wants to sit down and do three digit multiplication) and you mostly just do addition, just like above.
So say you’re doing 291 x 77 and you’re freaking out because that’s a lot of fucking lines to draw. So instead you use the lattice method. (Please forgive my shitty handwriting/line drawing abilities.)
You start out like this.
Draw boxes inside the numbers so that it’s three across and two down, and then draw diagonal lines inside the boxes. Follow? Great.
Now multiply each pair of numbers and write the product inside the box, like this.
Yeah, it looks scary, but take a couple deep breaths and have a look at the zoomed in version, which should be less scary.
See? Seven times seven is forty-nine, the tens digit goes above the diagonal, the ones digit goes below. Very simple, you can even manage it if you don’t know your multiplication tables (which was me until sixth grade, I know what I’m saying here). Not bad at all. But Moran, I hear you say, what if the product is smaller than ten? What do I put above the diagonal? You put a zero, or you leave it blank, but I like to put zeros because otherwise I assume that I forgot to fill it in, because I do that sort of thing a lot
Last step! Now you just add up the diagonals from right to left, like this.
.
That’s a lot of numbers. Don’t be scared. The first one on the right is easy: nine plus nothing is nine. Then you have nine plus four plus three: sixteen. So you write down the six and carry the one–see that little circled one up at the top of the third diagonal?
And then you end up with your final product, easy as lyin’.
Ta-da! It takes like less than three minutes to do three and four digit numbers, AND it’s easier to avoid mistakes than in long multiplication because it’s mostly addition.
And once you have some practice you can do this black magic, which took me about two minutes including time to draw it out and check it on the calculator.
(Source: yodiscrepo, via nowyoukno)
