Tag: math
wait is 5! = 120 an actual math thing i just reblogged it bc i sincerely believe that yelling a number makes it bigger
An exclamation point after a number means factorial. Five factorial is 5 times 4 times 3 times 2 times 1. Three factorial is 3 times 2 times 1, etc.
But the more exclamation points after a number, the less big it is, a double factorial is every other number, so 6!! is 6 times 4 times 2, which is less than 6!, So yelling a number makes it bigger, but yelling louder makes it smaller again
it’s because you scared it
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
why have we not alREADY BEEN TAUGHT THIS
Okay, so I’ve randomly browsed some of the comments and most people seem to be in awe of this, so I felt the need to explain. Let’s get ready for some MATH!
At heart, this is just basic multiplication, so I’d argue that your teachers did teach you this. It’s just got a different wrapping here; a wrapping that’s better suited to visual learners. This particular method is roughtly the equivalent of counting on your fingers to do addition. It works, but it gets messy fast and takes more effort in the long run.
That said, it is a good learning tool. Most people I know who were taught this learned it during one-on-one instruction because they were struggling with multiplication, which (I think) is the way it should be.
Explanation behind a cut because it got long.
To start with we have a picture that should convince you this concept is a visualization of multiplication. We start out with 3×2=6. Read that as “three by two” and the image might make a bit more sense.
The idea is that are three lines by two lines, which gives you a total of six intersections. I personally find boxes easier to visualize, so here is a picture of the same thing with boxes instead of lines.
And if you still don’t believe that lines can be used to visualize multiplication, here is a lovely example of 5×4=20 for you!
Aww yes, count those 20 dots.
Okay, next up we get to 32 x 12 = 384, which is a moderately more difficult problem because we’re no longer dealing with single digits. Below is an image comparing the line method from this post with the method taught in (American) schools.
As you can see, both methods get you the same answer. Notice any other similarities? Like maybe how the 6 and 4 become 64 and the 3 and 2 become 320 with a placeholder in the ones spot?
Maybe? No? Yes? Here’s another visual of the same problem, but with the extra step in there. See if it’s any easier to visualize this way.
Okay, so I’m going to assume that’s mostly self explanatory. You are visually creating the ones, tens, and hundreds places in columns on the diagram. You’re doing the same thing sans the visual on the right. The method taught in schools is more elegant, although both arrive at the same destination.
So can you do this while multiplying three digit numbers? The answer is yes, yes you can. Below is the setup.
It’s a little messier, and obviously this is a pretty simple problem, but it works. Just be sure to keep your columns from getting messed up. I like to do that with little dashed lines, which you can see below.
The answer to 112 x 231 is, in fact, 25872. So this works. It works as far up as you care to draw, but I’m going to stop at three digits.
So the next question is what happens when a column adds up to something above 10? Does this still work?
Well, yes, it does. Just not like this.
Each column on your diagram is the visual representation of a single digit in the final answer. So the first column is the ones place, the second is the tens, third is the hundreds, and so on. So what do we do when something adds up to over 10? We carry it over to the next column!
Tah-da! 858 is the solution to 78 x 11.
He’s another one, with bigger numbers. Also, this is why I say this method is a learning tool and not a feasible method of multiplication. Do you want all your homework to look like this?
I don’t. And I certainly didn’t enjoy counting those 72 dots off to the far right either, which I could have avoided if I’d known that that corner was 9×8, and 9×8 is 72.
So now we have three two digit numbers to add together using the principles I outlined in the previous problem.
So when we add them together as the ones, tens, and hundreds places, we get the answer. 78 x 29 =2262. Check on your calculator if you don’t believe me.
So we’ve figured out why this method works, and how to use it for bigger problems. Congratulations if you made it this far, and my apologies for the crappy handwriting and lousy quality of the images.
Yay math!
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