WTF why did no one mention this to me when I was struggling with math as a kid?
this post was submitted on 09 Nov 2023
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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
I'm confused again.
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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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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Seriously, why didn't anyone?! Would have made my life much easier.
they absolutely taught you the commutative property and transitive property
Yeah but they clearly taught it poorly
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... because multiplication is commutative.
69% of 420 is equal to 420% of 69.
So, is 289.8 the magic, double "nice" number?
Nice^2
Bro that's actually amazing
Idk if it’s the weed, the adderall, or the ADHD, but this thread is everything I need in my life.
33% of 7 = 7% of 33
Bitch, this only works for certain easy maths.
33% is the easy one.... 1/3 of 6 is 2, 1/3 of 1 is 0.33... 2.33..
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
That's pretty damned intensive for a trick that's supposed to make the maths easier.
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....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?
x% × y = x × y ÷ 100 This helps you out much more.
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
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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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
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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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Wait are you questioning the wisdom of panzer of the lake?!
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I read that now not for the first Time
I still dont believe it
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.
Nah, I prefer to treat my math problems like climate change. With denial.
6% of 100 is the same as 100% of 6.
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You could also do 6*50 and then divide by 100.
Why would I do that
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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Thanks Panzer
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.
Same energy as multiplication with 9, just take 1 from the right side and put it on the left
(09, 18, 27, 36, 45)
Instructions unclear...
09, 108, 1107, 11106, 111105
Keep doing this until you get a binary number and then your pc can do the rest for you
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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.
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