this post was submitted on 11 Dec 2024
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[–] SimonJ@reddthat.com 81 points 2 weeks ago (1 children)

Tell me you're not a dart player without telling me you don't play darts.

[–] Skua@kbin.earth 46 points 2 weeks ago (2 children)

Honestly I generally assume that everyone that isn't a slightly portly northern English man carrying a pint does not play darts seriously

[–] WaterSword@discuss.tchncs.de 12 points 2 weeks ago (1 children)
[–] vaultdweller013@sh.itjust.works 8 points 2 weeks ago (1 children)

Gen X Californians for some reason

Yakuza series fan.

[–] Infynis@midwest.social 2 points 2 weeks ago

You could also be a genetically enhanced doctor, taught by an Irishman

[–] MudMan@fedia.io 58 points 2 weeks ago (5 children)

I think it helps to remember that 3 times 7 is 21. When I think abotu that it looks less wrong.

It's the stupid seven multiplication table. Whatever glitch in human software makes it look so much less intuitive than all the others messes with so many other things that should be easy. I swear I struggle every time I have to look at it. I had to double check seven times three multiple times right now.

[–] Kichae@lemmy.ca 31 points 2 weeks ago (2 children)

I don't think that actually helps, because it's all vibes. 51 looks prime, because of no reason at all, and absolutely nothing looks like it should be divisible by 17, again, because raisins.

Knowing why it's true doesn't make it look right.

[–] elvith@feddit.org 17 points 2 weeks ago (1 children)

The digit sum of 51 is 6, which is divisible by three. So 51 is also divisible by three. It’s not even hard to see that it’s not prime.

[–] sugar_in_your_tea@sh.itjust.works 13 points 2 weeks ago (2 children)

Yup, my personal prime check is:

  1. Even?
  2. Ends in 5?
  3. Digits sun sum to 3?

If it fails all three and it's not an "obvious" prime (<20), then it's prime enough for me.

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[–] MudMan@fedia.io 3 points 2 weeks ago (1 children)

But I can wrap my head around that 51 is divisible by seventeen because of 21 and seven plus something that deals with the remaining 30 somewhere.

I know that's not how it works, but as you say it fixes my vibes when I see the 21 hiding inside the 51.

I'll say this: the other thing that makes this one a hard pill to swallow is that 17 looks way too big, and my vibes fix doesn't address that, but hey.

[–] sugar_in_your_tea@sh.itjust.works 3 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

Why not add the digits? If the sum of digits is divisible by 3, the number is divisible by 3. 5 + 1 is divisible by 3, so it's not prime.

49 "looks" more prime to me because it fails that test, and if I didn't know it's 7^2^, I'd say it's probably prime.

[–] MudMan@fedia.io 3 points 2 weeks ago (1 children)

I think the posts along these lines are already two steps too far away from the vibes.

Nobody is even considering the number being prime, it just looks like there can't be a round number of one against the other because one is big and ends in seven and the other is relatively small and ends in 1.

If you're even thinking about divisibility rules you're doing it wrong. As in, your brain is too impacted by maths to see what the numbers look like from instinct alone. There's no thinking in this, they just look weird together.

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[–] magic_lobster_party@fedia.io 12 points 2 weeks ago (1 children)

If there’s a number that’s the most oddball in the multiplication table, it’s 7.

It’s a prime number that doesn’t share any common divisors with 10, and isn’t adjacent to a divisor of 10 either.

2 and 5 are common divisors of 10, so they’re piece of cake.

3 is so small and close to 2, so it’s not too difficult to get.

9 is one off from 10, so it has a very predictable pattern.

4, 6 and 8 are even numbers, so they share common divisors with 10.

3 is easy because of the "digits sum to 3" trick, if you get stuck counting by 3s, it's easy to reset. Oh, and the proof for this is based on our 10-based number system, so your point absolutely stands.

[–] IndiBrony@lemmy.world 7 points 2 weeks ago

I have to remember it in patterns.

Digits go:

7, 4, 1

8, 5, 2

9, 6, 3

0

Tens go:

0, 1, 2

2, 3, 4

4, 5, 6,

7

Then my brain recognises everything else and I can't explain it properly 😂

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[–] spicytuna62@lemmy.world 29 points 2 weeks ago

299,999 is divisible by 7 and 17.

[–] ThisIsAManWhoKnowsHowToGling@lemmy.dbzer0.com 27 points 2 weeks ago (1 children)

100,000,001 is also divisible by 17

[–] pyre@lemmy.world 12 points 2 weeks ago (1 children)

I'm really starting to think this 17 is not a good guy

Just wait until you find out that 17 is divisible by 17

[–] TitularyDespotOfOstrich@lemmy.world 22 points 2 weeks ago (1 children)
[–] 50_centavos@lemmy.world 16 points 2 weeks ago (2 children)

So simple math problems are blowing people's minds now?

[–] dejected_warp_core@lemmy.world 15 points 2 weeks ago (2 children)

Always has been.

Just wait for the annual "PEDMAS vs PEMDAS" ~~discussion~~ flame-war on any major social media platform.

[–] ouRKaoS@lemmy.today 3 points 2 weeks ago

"Pedmas" sounds like a holiday for pedophiles...

End of debate.

[–] LifeInMultipleChoice@lemmy.ml 2 points 2 weeks ago (4 children)

Why? Not sure what the debate is, if you divide/multiply first?

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[–] affiliate@lemmy.world 14 points 2 weeks ago (1 children)

three is the first number that starts to cause problems.

Three is my favorite number, you take that back.

[–] PineRune@lemmy.world 13 points 2 weeks ago* (last edited 2 weeks ago) (3 children)

If it bothers your OCD, think of it more as (7x3)+(10x3)=17x3=51

[–] Cheradenine@sh.itjust.works 5 points 2 weeks ago (2 children)

Dude/ Dudette that's worse. 7x3=21, 10x3=30, 21+30=~~492~~ 51

That does less insane to the membrane

[–] JoMiran@lemmy.ml 6 points 2 weeks ago (3 children)

I see them as the same except that your way illustrates what his parentheses are doing.

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[–] ryedaft@sh.itjust.works 2 points 2 weeks ago

Nah, 45 + 6

153 + 23

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[–] superkret@feddit.org 12 points 2 weeks ago (1 children)

And 52 is divisible by 13.

[–] Duke_Nukem_1990@feddit.org 11 points 2 weeks ago

Somehow less offensive.

[–] petersr@lemmy.world 9 points 2 weeks ago

3 is the real culprit

[–] yarr@feddit.nl 9 points 2 weeks ago (1 children)

If it makes you feel any better, it's just (20 x 3) - (3 x 3).

I don't know why, but that makes me feel better.

[–] JasonDJ@lemmy.zip 9 points 2 weeks ago (1 children)

This must be the new math that parents are so scared of.

Back in my day, we multiplied 3 by 17 because that's how you do it. You multiply 3 times 7, you multiply 3 times 10, and you add. Simple.

Adding three to 17, to make it 20, multiplying that by 3, and then multiplying that 3 by 3 to subtract js equally valid, and easier to work out mentally IMO. It lays the framework for good estimation skills, too.

[–] PM_Your_Nudes_Please@lemmy.world 10 points 2 weeks ago* (last edited 2 weeks ago)

and easier to work out mentally IMO.

And this is the key factor to why math teaching has changed. Rote memorization is actually really really awful for learning.

Teaching math used to be a case of having students fill out their times tables. I still remember having to fill out this chart in under 5 minutes:

This was a quiz that we had to do multiple times per week. It was given to us blank, and 5 minutes obviously isn’t enough time to actually calculate everything; We were expected to have it memorized. And when the students had memorized the table, the quizzes changed into a series of small calculations from the table, again under 5 minutes. So if we ever had to calculate anything out, we could just refer to our memorized times table and pull the number off of that. But the issue is that this only works up to a certain point; Nobody is going to be able to reasonably memorize their times table beyond maybe 15x15. And this means that the times table essentially becomes worthless for doing math in larger numbers.

So instead, the “new” math teaches students how to take complicated problems (like 17x3) and break it down into easier steps. 17x3 is complicated, but 20x3 is just 2x3 with an added 0, and 3x3 is easy too. So if we can convert 17x3 into (20x3)-(3x3) then it becomes much easier to do in your head. Because not everyone can calculate 17x3 accurately, but virtually anyone beyond 1st grade can calculate 60-9.

The “new” math was developed by studying how the students who were good at math actually did their calculations. And it turns out, when you actually understand the concepts, you can create mental shortcuts to break the difficult problem down into a series of smaller problems. And that’s exactly what the “new” math does.

[–] Flocklesscrow@lemm.ee 9 points 2 weeks ago

Dart players know this

[–] ma1w4re@lemm.ee 6 points 2 weeks ago
[–] DogPeePoo@lemm.ee 5 points 2 weeks ago (1 children)

C’mon Chloe! This is 3rd grade math.

[–] spinne@sh.itjust.works 4 points 2 weeks ago

The information was there in front of Chloe and me this whole time, and still, we never realized

[–] Routhinator@startrek.website 3 points 2 weeks ago

This bugged me but then again

30 / 3 = 10 21 / 3 = 7

7+10 = 17

So yeah that makes perfect sense.

[–] TrickDacy@lemmy.world 2 points 2 weeks ago (1 children)
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[–] darthsid@lemmy.world 2 points 2 weeks ago

A bit random no?

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