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The panzer has spoken (sh.itjust.works)
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[-] DharmaCurious@startrek.website 197 points 11 months ago

WTF why did no one mention this to me when I was struggling with math as a kid?

[-] thisfro@slrpnk.net 127 points 11 months ago* (last edited 11 months ago)

They probably did, just not explicitly:

You could write (6*1/100)*50 = 6*(50*1/100)

It only uses the commutative property of multiplication and the fact that % is another way of writing 1/100.

Maybe also worth remembering that "x% of y" is just x/100*y

[-] ikiru@lemmy.ml 56 points 11 months ago
[-] Ravi@feddit.de 24 points 11 months ago

The word percent is exactly that per cent, which basically means parts of hundred. E.g. 10% are 10 of 100, or 60% are 60 of 100. You can also write this mathematically as 60/100 or 60÷100, which is 0.6.

Now in general: x% are x parts of 100 or x/100 or x÷100. If you want to calculate x% of y you just multiply it: y × x% = y × x ÷ 100.

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[-] Mewtwo@lemmy.blahaj.zone 6 points 11 months ago

I'm sorry but you have the big dumb

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[-] capt_wolf@lemmy.world 18 points 11 months ago* (last edited 11 months ago)

I totally remember being taught this. It's just way easier to break down percentages in terms of the nearest 1% or 10% times the number in the percent times the number you're taking the percentage of. You don't have to do the math for the 1 or 10 percentage as long as you remember that a 10% means move the decimal left once and 1% means move the decimal left twice. The rest is just basic multiplication.

40% of 59 = 10% of 59 times 4.

So...

4x59=236

or

(4x50=200) + (4x9=36)= 236

10% means move the decimal left once,

Therefore 40% of 59 is 23.6

With that you can easily do more complex percentages mentally like...

62% of 35 = 10% of 35 times 6 plus 1% of 35 times 2.

35x6=180+30=210 at 10% so 21

plus

35x2=60+10=70 at 1% so 0.7

Therefore 62% of 35 = 21.7

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[-] BaronDoggystyleVonWoof@lemmy.world 16 points 11 months ago

Seriously, why didn't anyone?! Would have made my life much easier.

[-] match@pawb.social 9 points 11 months ago

they absolutely taught you the commutative property and transitive property

[-] bingbong@lemmy.dbzer0.com 12 points 11 months ago

Yeah but they clearly taught it poorly

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[-] lolcatnip@reddthat.com 77 points 11 months ago

... because multiplication is commutative.

[-] saltnotsugar@lemm.ee 68 points 11 months ago

69% of 420 is equal to 420% of 69.

[-] ICastFist@programming.dev 35 points 11 months ago

So, is 289.8 the magic, double "nice" number?

[-] dditty@lemm.ee 12 points 11 months ago* (last edited 11 months ago)
[-] EvolvedTurtle@lemmy.world 54 points 11 months ago

Bro that's actually amazing

[-] jasondj@ttrpg.network 47 points 11 months ago

Idk if it’s the weed, the adderall, or the ADHD, but this thread is everything I need in my life.

[-] TryingToEscapeTarkov@lemmy.world 8 points 11 months ago

Weed and Adderall sound like a dope ass combo.

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[-] PunnyName@lemmy.world 43 points 11 months ago

33% of 7 = 7% of 33

Bitch, this only works for certain easy maths.

[-] dylanmorgan@slrpnk.net 55 points 11 months ago

29% of 29 is 29% of 29

Fuck, this trick sucks.

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[-] Girru00@lemmy.world 20 points 11 months ago

33% is the easy one.... 1/3 of 6 is 2, 1/3 of 1 is 0.33... 2.33..

[-] Sludgeyy@lemmy.world 8 points 11 months ago

1% of 33 is .33

.33 × 7 =

.3 x 7 = 2.1

.03 x 7 = .21

21 + 2.1 = 2.31

So

7% of 33 = 2.31

You could also do

33% of 7

10% of 7 is .7

1% of 7 is .07

So 11% is .77

.77 × 3 =

.7 × 3 = 2.1

.07 × 3 = .21

2.1 + .21 = 2.31

[-] PunnyName@lemmy.world 5 points 11 months ago

That's pretty damned intensive for a trick that's supposed to make the maths easier.

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[-] TAYRN@lemmy.world 29 points 11 months ago

....I mean, yeah? If the number is 50 or 10 that works out great. But let's try that with 7% of 13. Now it's 13% of 7. Just like you said, "much easier to calculate."

Okay, choosing prime numbers was intentionally mean on my part. But 3% of 9 becomes 9% of 3. 4% of 2 becomes 2% of 4. Can anyone honestly look me in the eye and tell me that this tip has helped them out in any meaningful way?

[-] Ravi@feddit.de 35 points 11 months ago

x% × y = x × y ÷ 100 This helps you out much more.

[-] plague_sapiens@lemmy.world 12 points 11 months ago* (last edited 11 months ago)

Its easier:

10% of a 100: 100 * 0,1 = 10

2,5% of 33: 33 * 0,025 = 30 * 0,025 + 3 * 0,025 = 0,75 + 0,075 = 0,825

Thats how I calculate it mostly in my brain. But being smart I usually just type everything (like 9*9) in the calculator xD

[-] Tikiporch@lemmy.world 22 points 11 months ago

Well, single digit percentages are easy. If it helps, move your decimal to the right so 9% becomes 90%. You can probably calculate 90% of 3 because you can do 10% and subtract it and get 2.7. Now move your decimal back to the left and you get 9% of 3 which is 0.27. You can do the same with higher percentages once you learn to break them in to 10% pieces.

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[-] hydroptic@sopuli.xyz 17 points 11 months ago

You're really asking whether commutativity of multiplication has ever helped anyone? Because that's what this is.

And yes it has helped me eg. estimate things or whatever along the years – but of course it's not going to be some sort of magical mathematics trick where just by reversing the numbers it'll always make things easier to calculate in your head

[-] TAYRN@lemmy.world 4 points 11 months ago* (last edited 11 months ago)

No, I think we all learned that multiplication is commutative in late elementary school, and obviously that's an important thing to know.

But I think the original post tried to make it out to be some magical mathematical trick, and I really don't understand that. Maybe I misunderstood the post.

Edit: wow, "commutative" is a really hard word to spell.

[-] hydroptic@sopuli.xyz 4 points 11 months ago

Yeah I think this is more about how you interpreted it, because it doesn't look like others took it as being an absolute magic trick rule and neither did I.

The Panzer of the Lake didn't use the word "commutativity" (fuck that really is hard to spell), but it gave out some wisdom that applied that rule by saying that "percentages are reversible": if the reverse of a percentage would be easier to calculate, you can use it and get the same answer. If it's not easier, well, then you're screwed 😁 Oooooor depending on the situation you can use the a × b% = a × b / 100 commutativity trick:

7 × 8% = 0.56

7 × 8 / 100 = 0.56

[-] TAYRN@lemmy.world 4 points 11 months ago

Oh, that is actually much more helpful. So, if you know your times tables, you can do percentages. You just have to use communitavatization.

Jokes aside, I really appreciate it. That made it much more easier to understand. Thank you.

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[-] BeardedGingerWonder@feddit.uk 16 points 11 months ago

I'd find 9% of 3 easier for sure. Sometimes it's easier sometimes it's not. Just use it when it's easier.

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[-] Goun@lemmy.ml 13 points 11 months ago

Wait are you questioning the wisdom of panzer of the lake?!

[-] Imgonnatrythis@sh.itjust.works 6 points 11 months ago
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[-] Feddinat0r@feddit.de 24 points 11 months ago

I read that now not for the first Time

I still dont believe it

[-] bus_factor@lemmy.world 25 points 11 months ago

You can work it out yourself. 6% is the same as 6/100, so 6% of 50 is (6/100)*50. Then do some algebra and see if you can jiggle it to say (50/100)*6. Then replace 6 and 50 with Greek letters so it looks more convincing.

[-] aksdb@feddit.de 8 points 11 months ago

Nah, I prefer to treat my math problems like climate change. With denial.

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[-] DharkStare@lemmy.world 19 points 11 months ago

You could also do 6*50 and then divide by 100.

[-] remotedev@lemmy.ca 8 points 11 months ago
[-] DharkStare@lemmy.world 14 points 11 months ago* (last edited 11 months ago)

In the meme example you wouldn't, but if you were trying to figure out Something like 2% of 5, it's easier to do (2 * 5)/100=0.1 then to do .02 * 5 or .05 * 2.

My comment was mainly pointing out that you can multiply those numbers in whatever order you want.

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[-] Teriyakiboy98@lemmy.world 17 points 11 months ago
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[-] nucleative@lemmy.world 17 points 11 months ago

Thanks Panzer

[-] HiddenLayer5@lemmy.ml 10 points 11 months ago* (last edited 11 months ago)

Also, a surprising number of people don't know that precentages are more often than not represented as decimals between 0 and 1 as opposed to actually a number out of 100 when used in calculations (because the concept of a percent doesn't really exist in math, it's just a context specific way of formatting a decimal). A lot of people just enter 69 when calculating a formula that operates on a precentage instead of 0.69 which obviously makes the formula useless, or if a formula is supposed to output a precentage, they assume that it output 0.69 percent instead of 69 percent.

[-] drew_belloc@programming.dev 6 points 11 months ago

Same energy as multiplication with 9, just take 1 from the right side and put it on the left

(09, 18, 27, 36, 45)

[-] bobzilla@lemmy.world 12 points 11 months ago

Instructions unclear...

09, 108, 1107, 11106, 111105

[-] drew_belloc@programming.dev 5 points 11 months ago

Keep doing this until you get a binary number and then your pc can do the rest for you

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[-] GBU_28@lemm.ee 4 points 11 months ago* (last edited 11 months ago)

You can multiply by 9 on your fingers.

Hold hands out, fingers splayed, thumbs towards each other. 🙌

9*2 put your left ring finger down (the 2nd finger). Left of that is tens place, right of that is the ones place.

So 1 on the left, 8 on the right of the downed finger.

9*5 put the left thumb down (5th finger.) 4, 5. 45.

[-] RobertOwnageJunior@lemmy.world 5 points 11 months ago

Instructions unclear, thumb stuck in asshole.

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this post was submitted on 09 Nov 2023
1378 points (98.2% liked)

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