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
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.
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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.
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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
Found the JavaScript developer
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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