Did you know?
Percentages are reversible. 8% of 25 is the same as 25% of 8, and often one of them is much easier to do in your head.
@fribbledom % is a mathematical constant equal to 0.01
It's obvious if you think about it, sure.
This is excellent news
@fribbledom I've been buried in vector geometry for the past day and this was the best math fact I've heard!
@fribbledom Wtf, never quite really realized it. I must've known but not this obvious. :D
@fribbledom 2nd grade knowledge. Why would you even post something so basic?
Please follow my secondary account @fribbledom_advanced_math where we discuss the Standard Model and the Callan-Symanzik equation 😄
On a more serious note: yes it's obvious if you think about it, but just look at all the replies and you'll realize why I post it.
Wow... I have seen many things before. I understand there are people who get a very poor education (and one toot about multiplication won't solve that), but to see how many people in here are proud of having a miserable education is truly staggering.
But be proud of whatever you want. As long as it doesn't affect your life, I don't care either.
@fribbledom holy h*ck that's useful, I never realized...
@fribbledom I've got one which I found out when drawing geometric shapes one day:
If you count up to a number from 1 and down again
1, 2, 3, 4, 5, 6, 7, 6, 5, 4, 3, 2, 1
Then all the numbers add up to the central number².
We were just doing this in class. For arithmetic sequences (where the difference between terms is constant), term n = a + d(n-1) where a is first term and d is difference, and sum to n terms is n/2(2a + d(n-1)). So I just applied those. It's fresh cos we just wrote a test on it haha
@fribbledom this is genius how did I not know this already
@fribbledom Oh my god, thank you so much !
@fribbledom so for that example, the answer is 2, right? I'm reallyvbad a maths, so I really want to be extra sure I understood correctly
@fribbledom then, why the frick didn't they teach us that at school? This would have saved me years of bother!!
Thank you for sharing. You have no idea how much this helps!
@fribbledom wow, thats awsome!
@fribbledom I have many such tricks. A bunch I use rely on 1/(1+x) ~= 1-x, when x is small (specifically, when x*x can be neglected). So, 18/19 = 18/(18+1) = 1/(1+18) ~= 1-1/18. 1/18 is close to 1/20 or .05. So 18/19 is about .95 (actually .947), and I did it entirely in my head without any actual division! (If you use this trick to approximate 1/18 = 1/(20-2)=1/(20*(1-2/20))=1/(20*(1-1/10)) ~= 1/20 * (1+1/10) = .055, you end up with .945. Again, these are steps one can do in one's head.)
@fribbledom Spot the typo. :) That first bit after 18/(18+1) should be 1/(1+1/18) not 1/(1+18).
@fribbledom what the FUCK
That absolutely makes sense and I had absolutely never thought of that.
@fribbledom NO i did NOT know that?!
@fribbledom I remembered that there was a trick like that, but for the last few days I was trying to remember Perfect timing thanks! (note that I didn't actually look into it, I was just lightly thinking about it)
@fribbledom you mean a*b=b*a or (a/100)*b=a*b/100 .. it sounds very boring stated that way.
I think this makes it a bit more readable:
a% of b = (a/100) * b = 0.01 * a * b
b% of a = (b/100) * a = 0.01 * b * a
Exactly. I don't know why it would be news that 8*5 is the same as 5*8 and just move the decimal place to make sense. People do this all day when out shopping don't they.
@fribbledom did u know? multiplication in the rational numbers is commutative, so 25/100 * 8 = 25 * 1/100 * 8 = 25 * 8 * 1/100 = 25 * 8/100 = 8/100 * 25.
@fribbledom also, it's important that the multiplication is associative, otherwise (25 * 1/100) * 8 = 25 * (1/100 * 8) may not be true.
@fribbledom I feel so sad that this has to be stated.
@email@example.com I did a bunch of math to check but holy shit thanks
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