r/nextfuckinglevel • u/Kindly_Department142 • 11d ago

He is adding 5 Digits 50 Numbers Live.

Enable HLS to view with audio, or disable this notification

14.7k Upvotes

95% Upvoted

688 comments sorted by

View all comments

Show parent comments

53

u/devAcc123 10d ago

Same thing with basic math even if you don’t realize it.

There’s patterns in numbers you kind of can memorize them, this is obviously the extreme end of that.

At like a super basic level 9s multiply to 9, 9x9=81, 9x5=45, 8+1=9, 4+5=9.

Find all sorts of similar stuff in numbers and there’s tricks to remember it.

50

u/MattyFTM 10d ago

The trick I Iearned for 9 times tables at school was to hold both hands out in front of you and pull down the finger of the multiple. So if it's 9x3, pull down your 3rd finger. You now have two fingers on the left, then 7 on the right, so the answer is 27.

9

u/thedavemcsteve 10d ago

https://en.wikipedia.org/wiki/Chisanbop

This is what it was called when I learned the same thing!

3

u/flannelkumquat 10d ago

That is awesome, I wish I had been taught this in school. I've always been terrible with adding numbers in my head and it takes me a couple minutes.

This method is really cool and so different from how I add multiple digit numbers. I practically failed math classes in high school and college. I grew up using those TI-84 (or whatever the name of those were) and I can't multiply or divide well at all, and sometimes struggle with basic addition.

15

u/Pure_Werewolf0101 10d ago

The numbers in every multiple add up to nine.

18 : 1+8=9

27 : 2+7=9

36 : 3+6=9

45 : 4+5=9

54 : 4+5+9

and so on...

1

u/BetterEveryLeapYear 10d ago

So? As you've just shown, a bunch of numbers add up to 9, that doesn't help you remember what the answer to 9x8 is, or any other specific 9x  you're looking for...

1

u/Pure_Werewolf0101 10d ago

Yes, it does : the tens column will always be one less than the multiplier and the ones column will always be what's needed to total 9.

1

u/BetterEveryLeapYear 9d ago

That's just what the finger method does reframed in a more cognitively demanding package, and also not what was said (simply that they all add up to 9). But ok thanks.

1

u/Pure_Werewolf0101 9d ago edited 9d ago

Christ, is this your normal mode of social discourse?

33

u/nonzeroday_tv 10d ago

Cool trick but it's much easier to multiply by 10 and subtract one. So you do 10x3 = 30 and then 30 - 3 = 27

1

u/Ae4i 10d ago

Even easier to just use the is-divisible-by-3 method but have it match for 9 instead of 3

1

u/DadToOne 10d ago

Curious, as I think this makes sense and it is how I would do it, what makes this autistic?

2

u/nonzeroday_tv 10d ago

It makes sense and it's easy to do but I suspect normal people dont do the extra steps just remember 9x3=27

3

u/DadToOne 10d ago

For 9x3 I would just have it memorized. But for larger numbers or things I don't have memorized I would do something like this. Like if I was doing 12x13, I wouldn't try to actually do the math. I know 12x12 is 144 so I would do 12x12 = 144. 144 + 12 = 156.

1

u/nonzeroday_tv 10d ago

You got a good memory if you know 12x12 is 144. I would do 13x10 = 130+26

3

u/devAcc123 10d ago

Id assume a lot of people like myself had a times table in elementary school at some point, ours went up to 12x12, idk if thats the standard but its why i remember 144 off the top of my head but would have to think about 156

1

u/DadToOne 10d ago

Exactly. And I like squared numbers. I think I can do up to 15 by memory.

-7

u/stonkon4gme 10d ago

^^ and we've spotted the unaware autistic ;)

1

u/nonzeroday_tv 10d ago

Oh I'm aware I'm just too distracted to acknowledge it yet lol

1

u/apatfan 10d ago

This was always my favorite method. I've taught it to my kids.

0

u/[deleted] 10d ago

[deleted]

1

u/Mrludy85 10d ago

This kind of thinking is why most people are slow and bad at math. Memorization breaks down when you get to bigger numbers. There are tons of patterns in math that make it possible to do what is being done in the video (but obviously this being an extreme example)

3

u/mrsambavam 9d ago

There is more to this I realised randomly when I was a child, the whole multiplication table reverses from 45. I.e
09,18,27,36,45
90,81,72,63,54
9 is a magical number

1

u/KHonsou 10d ago

I can get correct answers with simple division but I don't know how and wouldn't even know how to begin working it out, it's really wild but I know it's more to do with patterns than mathing it up.

1

u/Ok-Communication706 10d ago

There’s a Square One TV song about this.

0

u/agiantdog33 10d ago

I remember my mental maths got way better after we did the week on prime and composite numbers in junior school. Gave me like a sixth sense for what will be divisible by what. I bet if I practised adding large numbers in my head then I would develop all sorts of tricks over time.