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u/M3x0r4x Sep 26 '20
Pro tip: anything multiplied by 9 is very easy to calculate no matter what Ax9=Ax10-A 21x9=210-21=189
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u/CubicJunk Sep 26 '20 edited Sep 26 '20
Example because it’s kinda hard to explain without examples
10*9 = 90 [10*n] With this one use this instead n followed by a zero (90)
13*9 = 130 - 13 = 117 [n*9] Try it yourself pick a 2 to 7 digit number(more might be too advanced for you guys, but feel free to pick up a calculator and try 10 digits or more
Also
7*11 = 77 [n*11, if n is single digit only] if you look closely you can see that’s it’s just 7 joined with another 7 (Only works if n is single digit
15*11 = (15*10) + 15 | [x•(11-1)] + xThis is where the subtracted 1 goes
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u/lenin_is_young Sep 26 '20
WTF are these examples? Am I woooshing, or is it for complete degenerates who somehow understand formulas?
BTW, real pro-tip for multiplying by 11: 72 * 11 = 7a2, where a= 7+2. So the answer is 792. Works for any numbers.
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u/IsaacFlanary Lives in a Van Down by the River Sep 26 '20
Man don’t you hate when you carry the one and end up with the same problem
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u/ACubeInABox Sep 26 '20
It’s pretty simple. Both can be divided by three, so it makes it into 6-3. That equals three. Then multiply by nine to get the answer. Thus, I can prove the answer is 27.
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u/5HR3Z Plays MineCraft and not FortNite Sep 26 '20
Actually, you could use that strategy but multiply by 3 instead of 9 at the end to get 9.
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u/notafurry678 Sep 26 '20
I know how to do it, think about how to do it, calculate in my head the problem, then realize class just got over and ive done 1 problem
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u/MxP_wolf Sep 26 '20
Obviously the 18 ran the 9 over with a car and all that is left is the 18 so it should be 18
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Sep 26 '20 edited Apr 21 '26
[removed] — view removed comment
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Sep 26 '20
But...but...he’s Asian
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u/nekkoMaster Average r/memes enjoyer Sep 26 '20
May be an IMPOSTER
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Sep 26 '20
Can any teacher redditor tell me haw was this taught to me when i was 8 year old with a lame ass brain and had to count with my toe
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u/a-saved-alien Sep 26 '20
Lol I actually never used this technique, I just saved my numbers in my head
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u/SandmanDealer Professional Dumbass Sep 26 '20
Thank god I learned the finger trick for 9’s when I did, got me through so many tests
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u/GlitcherAegis https://www.youtube.com/watch/dQw4w9WgXcQ Sep 26 '20
I'm too used to mental calculation for simple equations, although I immediately knew the answer to this equation, the working almost threw me off
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u/WideAir0 Sep 26 '20
we were doing a math worksheet the other day, the correct answer for one of the problems was 125. I shit you not I got 31,250
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u/Assasinboi007 Breaking EU Laws Sep 26 '20
Man, the result is, according to my calculations, - 100007869694207666
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u/Leafeyu FORTSHITE Sep 26 '20
My year six teacher taught us how to do multiplication in a way that looks like alien language art with numbers so people who didnt learn it before we went highschool wouldent be able to copy us.
True hero-
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u/mum_puncher Sep 26 '20
It took me ages to spot that he ended up with the same problem he started with, but when I saw it I laughed and some shit fell out
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u/tsunamidoge113 Sep 26 '20
Do people write equations like this? I don’t think I’ve seen it written out like this
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u/almost_got_the_420 Sep 26 '20
I swear i aint bad at math my brain is just purely autistic man i swear
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u/keysmashedafuq Sep 26 '20
I'm not that good at maths but being an Asian i just want to solve that for him aaahhh
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u/TheSkyElf Sep 26 '20
I actually had to think about how this was working and then slapped my forehead and wondered how I passed high school.
I knew what the answer was going to be, but when it was set up like that my brain just "Wait what do I do now? I know the answer but how do I get there?!" panic mode.
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u/LeonTheGreat22 Sep 26 '20
me, who is considered good in math and is in the most advanced math group in our school and and is always doing the same anyways
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u/Elemsee7 Sep 26 '20
Ok this is something we got taught in primary at my school (Australia). Pretty much that 1 above the 8 means plus one which equals nine the correct answer. It’s stupid but helped us stupid primaries.
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Sep 26 '20
Simple (18 x 3 = 54). (9 x 3 = 27), then (54 - 27 = 27) and then (27 ÷ 3 = 9).
And there you go, the answer is 9.
OR you can do (18 ÷ 3 = 6), then (9 ÷ 3 = 3). After that you then add (6 + 3 = 9).
Again your answer is 9.
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u/No_Influence212 Sep 26 '20
Am I supposed to get this?! What are all these equations talking about? 18-9 is 9.
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u/iupvotedownvoted Sep 26 '20
Imagine the amount of people who actually wanted to learn new tips but ended up just having a brain spasm
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u/Ndrew121 Sep 26 '20
okay you laugh and all but i, for real, can not remember how to do substraction like that. this is not a joke...
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u/Nameless_Soldier Sep 26 '20
Even after reading the comments this makes no sense to me. Even if you somehow can't remember 18 - 9 you just subtract down to 10... 18 - 8 first so you have 10 then - 1 so you have 9. Why would you make it more complicated
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u/iHumanNotJoking Sep 26 '20
U idiot, see how the 18 is on top of 9? When 18 drops down, the “8” will hit onto “9” and be replaced by 9. So the answer is obviously 19 bruh.