Do kids not get taught the 9 x “trick”?
Posted by GRMAx1000@reddit | AskUK | View on Reddit | 149 comments
[removed]
Posted by GRMAx1000@reddit | AskUK | View on Reddit | 149 comments
[removed]
Wild_Beginning_4032@reddit
Or you could just times by ten and take the object number away from the product.
387380@reddit
Learning tricks does not help times table recall, it actually hinders it. They just need to be learned until recall is automatic. Like most calculations we do IRL they are just part of a wider numerical problem or question, so speed is key in order to be able to answer a wider problem
Slothjitzu@reddit
That’s the opposite of the way it works.
You don’t need to memorise, you need to learn how to do it.
It’s just that the trick OP is talking about isn’t a great one because it literally only works with 9s, and only up to 9x9.
Ideally you’d learn how to multiply by easier numbers and then work out more difficult numbers from there.
Like if you struggle with 9 x 15 then you need to do 10 x 15 - 10 instead, or 9 x 5 + 9 x 10.
tinersa@reddit
how would you suggest learning how?
LactatingBadger@reddit
If I ask you what 4x2 is, do you go through some process or do you just know? You need to know how to do it so when given an arbitrary sum you have the tools to do it, but memorising a small set so the answer is reflexive is also extremely useful.
387380@reddit
I disagree for multiplication of single digits. The knowledge of these is the gateway to understanding how to perform multi digit problems. As a primary school teacher there is nothing worse than seeing a student floundering through a multi step problem calculating 4 x 7 then losing their way in the context of that problem. The key for me is always learn them early and help open the world of problem solving through understanding how to apply the knowledge.
LactatingBadger@reddit
I don't disagree that they should know how to reason through the problem. On that front I 100% agree. When I'm tutoring I always try and take the time to find a way to work through the problem that is intuitive for them and that allows them to not just get the answer, but feel like they really get how they got there.
My point is that it is also worth having a small bank of multiplications learned reflexively. That way when you're working through a harder problem you can just short circuit the trivial operations and focus on the larger problem.
thegentleduck@reddit
Recall is a shortcut that hinders better learning of maths. I'm not saying it's useless - knowing x*y for all integer values of x and y between 1 and 12 inclusive is useful - but the tricks are far more widely applicable.
Being in the habit of "9 times is 10 times minus 1 times" will help you solve 923 or 94897, and the logic of "multiply something easier and subtract" can work even more widely, to things like decimals.
I disagree that "speed is key". Understanding is key.
Kamila95@reddit
I am 30 and the x9 finger trick carried me through life, including taking applied maths at university.
RiverGlittering@reddit
When I was at school, I wasn't taught any tricks for multiplying.
It was just repeating the times tables over and over, until it stuck in your head. As a result, many people can do 1 - 12s when counting up, but struggle with 13+.
And many people wouldn't be able to just answer 6x7 without counting up the table.
Brilliant-Figure-149@reddit
Same here. No tricks, just remembering stuff. Those were the days.
LasagneSiesta@reddit
Remember you won’t have a calculator in your pocket when you’re older
Best-Research4022@reddit
No calculator needed, say 9x4 put down your 4th finger on your left hand, numbers before that finger are the tens and after on both hands are the single digits works for all 9’s as long as you still have all your fingers
xX8Havok8Xx@reddit
Ok 49×9
LM285@reddit
Former maths teacher here. That works and is good to know in a pinch, but isn’t a good way for most people to do arithmetic.
In fact, I’m wary of ‘tricks’ in general. Simple Arithmetic is largely memorisation. It’s why darts players are often great at subtraction- they do it over and over again.
In the end, everything relies on a base of memorisation - you know instinctively that 2+2 is 4 and you don’t have to think about it. So 12+2 becomes easy.
Arithmetic builds up the level of instinctiveness. If you know that 67 is 42 off the top of your head, the 607 is also easier. 597 is also easier too: 607 - 7 =420-7=413.
ActualArgument8926@reddit
I agree that these kind of "tricks" are not the best, but on the other hand memorising all of them is also bad. My go to was to break them down to something that easier to remember. Like n*9=n*10-n and 6*n=5*n+n
aaeme@reddit
That the digits of any multiple of 9 adds up to 9 is an interesting fact as well as a a useful trick though so worth teaching I think.
I believe the same is true for any number 1 less than the base (i.e. the maximum digit in the base), so e.g., the digits of any multiple of 15 (F) add up to 15 (F) in hexadecimal.
But otherwise agreed: memorising some starting points allows us to do mental arithmetic at all and the more the faster.
garethchester@reddit
Heads up that the asterisk has really messed you over there
LM285@reddit
Thanks!
Capable_Life@reddit
My maths teacher told us about an old student. Terrible at maths, absolutely hopeless. However, the student worked behind the till in his parent’s shop on the weekends. He spent so much time calculating customer’s change that his basic arithmetic became near instantaneous!
WillowCreekWanderer@reddit
My year 4 teacher was absolutely insistent that we have "rapid recall" of all the multiplication tables up to 12. Every so often during a lesson, she would randomly call out a sum, point at someone, and whoever she pointed at would be expected to answer without even thinking about it. I hated it at the time, but I've got to admit it was effective
Own_Glove845@reddit
When I did O levels we didn't even have calculators. We had slide rules and log books.
PaleKey6424@reddit
I was told that in 2015💀
SmashNit@reddit
Hope your response was you pulling your phone out and typing in 55378008
sf-keto@reddit
My oldest cousin was actually taught to use a slide rule in school!
Even then, people used mechanical tools.
TannedCroissant@reddit
I have a calculator on my wrist that accepts voice commands.
nanakapow@reddit
2659004 x 2
andywarlol@reddit
Giggity. Hehe.
iwantauniquename@reddit
Yeah in second and third year juniors (so yrs 5 and 6 but this was early 80s) our first daily task was to write the times tables 1 to 12 forwards and backwards on a postcard size piece of paper. The main problem was hand cramping. As a result these are just part of the number system for me, I know them as well as I know 5 follows 6.
You can't really appreciate the rest of maths until you have this built in
MrDannySantos@reddit
Can't believe you chose 6 7 as the example...
Melodicmat@reddit
lol, imagine trying to teach a bunch of kids how to work out 6x7, and as soon you say it, they all start doing that "six seven" thing with their hands and laughing non stop lol
RiverGlittering@reddit
I was going to choose 7x8, but I decided that was easier than 6x7, and I'm not entirely sure why.
WillowCreekWanderer@reddit
7x8 was my favourite multiplication when I was at primary school, and to this day I have absolutely no idea why
zlukes@reddit
We were taught it by singing 5,6,7,8 (to the tune of the song by Steps) so 7x8=56
WillowCreekWanderer@reddit
Oh, that's a good one!
cfehunter@reddit
No but most can do 5x7 instantly, then you just add 7.
bacon_cake@reddit
I just did it in my head and did 3 x 7 and doubled it.
cfehunter@reddit
same thing pretty much. The norm seems to be that people memorise a subset of the tables and then do easy steps to get to the others.
dayvie182@reddit
That's literally how my brains works with these multiplications.
clrthrn@reddit
I sent my worried daughter into a school exam today telling her if she can remember some of her tables then addition/subtraction will save her arse from there.
meadowender@reddit
Me too, late 70's, it was always the 1-12 times table, it never, ever went to 13. I 'm not sure the teachers could count to 13 though
Stralau@reddit
The simple trick to remembering 6x7 is reading or listening to the Hitchhiker’s Guide To The Galaxy, surely?
Throwythrow360@reddit
It's 6x9=42 in the book so that might not help too much...
GRMAx1000@reddit (OP)
TBF I explained fronted adverbials to an English friend today and we realised that as women schooled in the 80s, I had learned more English grammar “rules” than she because I grew up in Ireland and that’s how we were taught. I don’t think knowing those rules necessarily makes me “better at English”. However, my personal experience of sums is that basic mental maths makes my life easier
RiverGlittering@reddit
I have absolutely no idea what fronted adverbials are, though if I had to guess they are adverbs pushed to the start of a sentence.
This is a problem I had with learning German. They'd compare rules to English grammar rules to make it easier for me, and I'd be totally lost. I don't know those rules, I just know English.
GRMAx1000@reddit (OP)
English is my first language but I also learned Irish, German and French and have a smattering of Italian. My partner refused to keep doing Spanish Duolingo with me because I kept skipping ahead claiming it was too easy 🤓
And you’re completely correct about fronted adverbials. When the term was introduced to my English 9 year olds I threw my toys out and said “oh ffs - just say adverb at the start and stop making it EVEN more confusing than it needs to be”
Salaried_Zebra@reddit
I honestly don't know why kids today need to be taught that. A few months ago my 6yo said to her cousin, "What's your favourite split digraph?" and I had to question why that's terminology that a 6yo need to know.
Same as this phonics stuff - fine with the principle of it but why are we failing schools whose pupils try to 'correct' nonsense words (to be clear I couldn't give less of a fuck if my child gets every question wrong in every paper right up until the only ones that matter)
Conscious-Ball8373@reddit
If your cold gets every answer wrong on every paper before the ones that matter, they're not going to suddenly be brilliant at the ones that matter and do well at them. The point of the standardized tests in schools is to identify early the children that need extra help and try to get it to them.
When one of our children started school, we had a meeting with her teacher about reading where she explained the system they use to teach it. I remarked that it seemed to change every few years and yet we had all learned to read. Her response has stuck with me -"Yes, you could probably learn to read no matter how you were taught, and the way you were taught is fine for probably 97% of children but we keep changing it to try to make it better for the 3% who really struggle and to give them a better chance." That seems worth doing to me.
Salaried_Zebra@reddit
If that was really what they used it for, I'd be more supportive. All too often they're used as sticks to beat schools with.
As I said, I take no issue with using phonics method - I take issue with the check being scored on nonsense words.
Conscious-Ball8373@reddit
But that's a good thing if you look at it another way. If a school's SAT results are consistently below par, doesn't that tell you that the school is doing something worse than other schools and something needs to change? Why should we put up with children in a particular area being disadvantaged because their school isn't well-run and they're not well-taught? Too often schools look at poor SAT results, shrug and say, "There's nothing we can do." Too often what that really means is, "We've tried nothing and we're all out of ideas."
"sticks to beat schools with" is really the same process as seeing which children need help and getting it to them early - it's identifying which schools are not teaching effectively and trying to change that. That the schools resist change and see it as just beating them with a stick is part of the problem.
Conscious-Ball8373@reddit
I learned some grammar when I was at school and thought it was stupid.
I was grateful for it, and learned far more, when I started learning other languages later in life.
Grammar is the language we use to talk about languages. It is very difficult to explain one language in another language, to say what is similar and what is different, without it.
iamabigtree@reddit
Right. I learned far more about English constructions when learning French and Spanish for myself.
Neither_Process_7847@reddit
Works in language - one reason why English people often at least used to struggle learning other languages was they weren't taught the rules of their own (admittedly they're fuzzier than many other languages') so couldn't easily map the grammar they learned onto what they wanted to say.
Khaleesi1536@reddit
I have to say, learning grammar rules etc while learning Spanish made me so much better at understanding how English worked
portablekettle@reddit
Same lol. All the way through school they gave us multiplication grids constantly but as the lessons went on they'd up the amount of numbers on them
northyj0e@reddit
Holy shit if it had been like that when I was at school, I'd have had no chance. I still do those tricks (do 2x, 5x, 9x or 10x and add or remove as necessary) now and have to calculate, rather than recite all multiplications. Honestly I think memorising the tables only works up until 12x12, after that, if you don't have the tricks, what do you do?!
StatisticianUsual471@reddit
They told us it existed but they told they weren't going to teach us it for some reason I can't remember
roxieh@reddit
I didn't know the "trick" in OPs post either but I was taught how the up to ten times the answers start flipping. Eg 9, 18, 27, 36, 45 (flips here after 5x), 54, 63, 72, 81 and 90 at 10x. 9s are weird. Knowing that all the answers add up to 9 is also neat!
iamabigtree@reddit
Yes repeating over and over and remembered none of it.
xX8Havok8Xx@reddit
9 is the easiest. I always just do X × 10 - X.
So 9x6= 60-6
magical_matey@reddit
The real trick is you going to Kumon maths class for years 🥲
tyger2020@reddit
IS that a trick?
An actual trick is that if you put your finger down you get the number anyway.
If you want to know 9x3 put your 3rd finger down from the left and you're left with 2 fingers, a gap, and 7 fingers. This works from 9x1 to 9x10.
stopismysafeword@reddit
Teaching kids these trick makes math more enjoyable and therefore easier, I'm not good at it and know that it's a difficult subject for lots of people and this kind of thing can really help, but instead it's just do the times tables in order 100 times until you remember, oh and whenever you need to multiply something you'll have to do that in your head every time. I hope it has improved since I've left school.
I understand there is a need to understand the how rather than just knowing a trick to work something out, but multiplication isn't complex maths and all people need to understand is that 9x6 is 54 and that it is because it's 6 multiplied by 9.
Plannet_Depressed@reddit
For 9 each answer ads to 9
2x9 = 18 [1+8 =9 or take 1 off the x so 2x9 its 2x so it's 1.. 1+8=9.. 18] 2x9=18
7x9 [7-1 = 6.. 63 6+3=9]
7x9=63
27x9 [20 -0 =2 2x9=18 +0 =180] [7x9 -1=6 63..] 180 + 63 = 180+60[240]+3
27x9 = 243
Kimbo-BS@reddit
Never learnt that and it seems no less complicated that just multiplaying by 10 and subtracting the multiplier of the 9.
Also, children that get 9 x 3 wrong probably aren't going to get "9 x 6 means the answer starts with 5 and the sum of the answer will equal 9" either.
spikeboy4@reddit
Tbf this is talking about year 4 kids, so the rule may be a tad complicated for them
DanielReddit26@reddit
😅😅😅
Salaried_Zebra@reddit
I'm 38, I wasn't taught that trick. I was taught "up one, down one" for 9x - so your tens goes up one from the previous answer, and the units goes down one. That gets you to 9x10 then the cycle begins again.
ameliasophia@reddit
That works for counting up in nines but if you get asked one at random like 7 x 9 then doing the one less and what’s missing to make nine is probably quicker than counting up in nines
amBrollachan@reddit
I was taught the multiply by ten and subtract the number trick. So 7 x 9 is 70 - 7.
MarkWrenn74@reddit
Is the trick the one with your fingers? Like if you want the answer to 9×7, you bend back your 7th finger (the second finger on your right hand), leaving 6 before it and 3 after it: 63
LightBylb@reddit
I have a math alarm and use this every single morning
MarkWrenn74@reddit
I've never heard of the concept of a “maths alarm”. What does it do? Wake you up in the morning by asking you to solve an algebraic equation? 😂
spoo4brains@reddit
I learned the finger trick but have never used it, I just multiply by 10 and take off the number you were multiplying if I don't know it automatically.
MarkWrenn74@reddit
That's handy. Good tip
GRMAx1000@reddit (OP)
Yes but ALSO 6 + 3 =9. The sum of the parts is always 9 so you can check your answer.
9x13=117
1, then 1+7=8
1+8=9
Or 1+1 =2 + 7 =9
MarkWrenn74@reddit
Quite right. Any multiple of 9 has figures that can, eventually, add up to 9
PassiveTheme@reddit
This works because it's also true of multiples of 3 - they will add up to 3 (or 6 or 9)
TheShakyHandsMan@reddit
What about 2x3?
Smeeble09@reddit
That's the one I know, and have already taught it to my daughter.
doctorgibson@reddit
What if I want the answer to 9 x 11, do I bend my 11th finger?
tobotic@reddit
You use the eleven times table trick.
Lucky-Condition9245@reddit
Socks and shoes off
faa19@reddit
I still use the finger trick as a sanity check. I've been an accountant for over 20 years.
_Pencilfish@reddit
I'm sorry, but this (times tables, memorisation, or multiplication "tricks") is simply a waste of time. Being able to multiply numbers quickly is a fun party trick in today's world and nothing more. I say this as someone who's just spent four years studying a maths-heavy STEM course.
I hated times tables as a kid. I was bad at them and couldn't see the point. Nearly decided that I hated all of maths. Fortunately, my mum started to teach me "real" maths - equations and algebra, which is the stuff people actually need to know in maths-heavy subjects.
NoExperience9717@reddit
Up to 12 x 12 does have real world use as you can guesstimate ballpark figures a lot of the time for real world data.
Serberou5@reddit
610-6 is the way I was shown to do 69 quicky as 10 is a much easier number to work with.
Justboy__@reddit
That’s how I would do it, I don’t really understand what OP means when they say 9x6 means the answer starts with 5?
SlightlyWarmAnt@reddit
Whatever number you are multiplying 9 by, you minus 1 and that's what your answer starts with.
For example,
9x7 means the answer starts with a 6 9x4 means the answer starts with a 3 9x8 means the answer starts with a 7
Then of course you just put whatever number adds up to 9 as your second number on the answer
9x7 answer starts with a 6 then you would put a 3 on it to get 63 9x4 answer starts with a 3 then you would put a 6 on it to get 36 9x8 answer starts with a 7 then you would put a 2 on it to get 72
It sounds complicated when writing it out but it's very simple once you learn the method and can do it without thinking.
Shed_Some_Skin@reddit
This stops working after a point. 9x65 is 585, for example. It's fine enough for basic times tables but it's a poor rule to teach if it doesn't scale
(10X)-X continues to work, though
Justboy__@reddit
Ahhh ok, I get you, thanks.
SlightlyWarmAnt@reddit
No problem. The formatting on my comment doesn't help but I'm glad you are now aware of another one of the many methods :)
Xaarock@reddit
What they're saying is that the two digits add up to 9, and the first digit is one less that the number you are multiplying by. So in your head you can do for example 6x9 -> 6-1=5 (first digit) plus 4 (second digit) is 9 -> 54
Justboy__@reddit
Thanks, get it now it’s been explained, I’ve just never been taught it that way before so it wasn’t making any sense without context.
PeteWTF@reddit
The 10s column starters with the number 1 below what you are multiplying by and the total adds up to 9
So 1x9 = 09 2x9 =18 3x9 = 27 ect.
Holty12345@reddit
I’ve also never heard 9x6 means it starts with a 5 - but new each multiple digits adds up together to be 9. but i guess the two methods here are on the same track.
Like you know 6x10 equals 60
Then 6x9 would be somewhere in the 50s because you know it’s under 60 due to times 10.
busbybob@reddit
Didnt know this trick. I learned 9x table by knowing what 10x the value was and then subtracting the value
AnonymousTimewaster@reddit
Why would you just times by 10 and take the digit off?
MrDibbsey@reddit
I've never been taught tricks of any kind, we were taught the Array method for multiplication, and for any larger numbers I'll do some varient of that in my head. For smaller numbers, I'll break it down into ones I can do easily and then add on the remainder.
If I were to do 73*54, I'd run through the following,
7*5*100=3500
7*4*10 =280
5*3*10 =150
3*4 =12
Sum =3942
And for 8*12
10*12 =120
-(2*12) =-24
Sum =96
shortercrust@reddit
We didn’t learn times tables at all when I was at school in the early 80s. We didn’t get taught formal grammar either. I think all that stuff was deeply unfashionable at the time. Still, for some reason the 9 times table is the only one I know by heart. I think I liked the pattern of it - first digit counts up and second counts down.
Vehlin@reddit
Urgh. Learning German while having no idea what a grammatical case was was fun.
shortercrust@reddit
Yeah exactly! They were right in that kids don’t actually need to be taught grammar to learn English but it makes learning foreign languages much harder later on. I only got a proper grasp of formal grammar when I trained to be speech and language therapist at university.
SnooDonuts6494@reddit
Maybe you mean "I trained to be a speech and language therapist".
shortercrust@reddit
Ah, I've just realised you trawling thought my comments to make snarky replies. Classy. And blocked.
SoylentDave@reddit
I was at school in the early 80s and we absolutely did times tables (grammar, and specific lessons on cursive writing)
Your school might have been crap.
Smiley_Dub@reddit
LOVE THIS!! 👏👏👏
WillowCreekWanderer@reddit
Does anyone remember a poem about a kid who learns the answer to 6x9 by calling her doll Fifty-Four all day? A girl at my primary school recited it for the school talent show about 20 years ago, and for some reason I've never forgotten either the poem or the sum
ben_jamin_h@reddit
9 X 6 means the answer will start with 5 and the sum of the numbers will be 9....
What?
9 X 6 = 6 X 10 (60, easy) - 6 = 54.
Why are you making it difficult with that weird trick?
Multiplying any number by 9 is just multiplying it by 10 (so easy) and then subtracting one of that number (so easy)
CactusClothesline@reddit
I've never heard of this trick but surely the easiest thing about the nine times table is you just times it by ten then take itself away from that answer.
de-tree-fiddy@reddit
My mum made me recite my 3 to 9 times tables once per week for about 7 years.
Fire_Shin@reddit
You can do most of 9's table easily. Just write the numbers 1 through 8 descending. 1 2 3 4 5 6 7 8
Then write 1 through 8 ascending next to the first number. Look familiar? :)
19 27 36 45 54 63 72 81
wotsit_sandwich@reddit
I still use the fingers trick for 9 x something
merp1991@reddit
I was never shown any clever tricks in school but I did end up learning a few times tables, and for some reason I know my square numbers up to 16, so I can fill in the gaps quickly enough to get what I need.
MonsieurGump@reddit
Op- “Surely 9 is the easiest times table after 10, 5 and 2”?
11- “Hold my pint, mate”
Mascbox@reddit
If you can't remember the times tables themselves then it's pretty unlikely that you'll even remember the trick.
Plus, Applying the trick probably requires more cognitive steps than trying to work out the timetable in situ.
gnomeplanet@reddit
9 x 12345 = 111105. 1+1+1+1+0+5 = 9
Resident-Total-1194@reddit
If people don’t spot the 9 x 6 means the answer starts with 5 and the sum of the answer will equal 9, why isn’t it pointed out? Surely 9 is the easiest times table after 10, 5 and 2??
I have never heard of this nor understand it
depressedblondeguy@reddit
Where I went to school, we didn't start learning the times table until year 6
SunSimilar9988@reddit
0 and 1 might be easier
BlackberryMelodic567@reddit
The way i learnt was "Oh its 09, 18, 27 - wait are the one collumn going up and the tens going down? Oh this is easy"
Organic-Can7856@reddit
I retired 6 years ago for you a back injury but I taught my pupils the finger trick.
Corrie7686@reddit
I wasn't taught that, my generation was taught during a period that they had dropped times tables and tricks. Although I did make my own. 9 x anything is easy, just times by 10 (add a zero) and remove the number. 9x 8 is 80 - 8 i.e. 72. Same concept works (in my mind) for 11 times and 8 or 12 times.
BasisOk4268@reddit
I was never taught any tricks for multiplications tables, but I figured some out on my own. For the 9x table I just take the 10x, so 10x6=60 and take away 6 = 54. Repeat as needed.
GRMAx1000@reddit (OP)
My son who is doing maths and physics A levels just told me he still doesn’t know his times tables. I have learned a lesson in how brains work. 😂
cateml@reddit
To be fair I teach physics and my “mental arithmetic” level is shockingly bad. (ADHD and dyslexia, fun times.). But it’s fine because calculators exist. I’m upfront about it, I’ll be making up examples on the board and go “right someone give me the answer to this [basic mental arithmetic], I’m not doing it”.
For a while they think I’m having them on just to test that they’re listening. And I mean, that is a silver lining. It sometimes takes them a while to realise that I actually don’t know.
scuderia91@reddit
I’m an engineer and can’t do times tables despite completing a full engineering degree. And it’s because I’ve never needed to, I can use a calculator or excel to do any of the maths I need.
deadeyes1990@reddit
9x6 being the one that gets everyone is so fair tbh. 54 just doesn’t feel like it should be there. Dodgy little number.
The 9 trick should definitely be taught though. Not in a smug “how did you not know this?” way, just in a “here’s the little cheat code that makes your brain stop panicking” way.
Maths is a lot less horrible when someone actually shows you the pattern.
ddmf@reddit
We did the finger trick for 9 x - for 5x9 for example lower the 5th finger, the answer is the fingers up to the left as 10s and what's left to the right as units.
Zandercy42@reddit
I didn't get taught this 20 years ago either
CaptainHindsight92@reddit
I multiply by 10 and remove one of the number so 9x6 is 60-6. I don’t know but it is easier, especially with big numbers so 220 x 9 is 2200 - 220 which is 1980. Im not sure if your trick works for that?
love_in_october@reddit
It's harder and takes longer to remember and apply the rule than memorise the answer. There are only twelve numbers in the taught nine times table.
newtonbase@reddit
At 53 I've just found out that there's a 7x trick too.
cfehunter@reddit
The only trick I learnt for 9's was to just subtract from the 10's.
Sapling13@reddit
11s are easy too, obviously. But a nice trick for 11 x (double digit number) is to split it and add. For example, 11 x 43 = 4_(4+3)_3 = 473.
Sapling13@reddit
I was teaching my daughter this trick on Monday. She’d never heard it before - blew my mind.
occasionalrant414@reddit
I learnt the times tables, I remember Mrs Pritchard and Mrs Tagg shouting at us if we got it wrong when made to recite it in front of the class.
1-12 is not too bad (I mentally go up the tables) but after that it gets a bit more challenging. I'm 42 and honestly finding out tlwhat 12x79 is rarely comes up and if it does, well fuck you Mrs Tagg as we DO have calculators with us all the time.
macisnotonline@reddit
I learned my 9x tables by my teacher pointing out that as the first number increases by one the second decreases by one. 18, 27, 36 etc.
I’m 90% sure I have discalculia and im terrible at maths but I’m usually ok with nine times something because of this
Davan94@reddit
I worked as a maths teacher for a few years (left it a couple of years ago due to stress), and there was a strong focus on teaching understanding not tricks. The idea being that if students understand the mathematical principles and reasons for how/why things happen, they'll be able to apply what they've learnt in more areas.
Gauntlets28@reddit
One digit ascends as the other descends. Don't know if it was taught to us as such, but I definitely knew it quite early on.
Bowdin@reddit
I can't remember my times tables to save my life.
I just calculate things as quickly as I can in my head.
I personally feel like the memory aspect of the times tables isn't very useful and kids should be taught better ways to do mental maths instead.
Not to mention the abolition of teaching memory skills like image linking means kids don't know how to remember things very well either.
Kapika96@reddit
What trick? Just x by 10 then minus 1?
lardarz@reddit
i never learned that and those are the ones my kid struggles with.
in my head I do 6x10 and then minus 6, but I'll try this to see if she gets it
usernameinmail@reddit
Yeah I remember being taught this in primary
PaintSniffer1@reddit
no I was taught to just work it out
jordsta95@reddit
I don't remember being taught it. All I remember is doing times tables in primary school.
But I did realise the 9x "trick" in year 5 or 6 without being told it.
And even into the much larger numbers, it's a quick sanity check that the numbers should always be a multiple of 9. Whether it's 9*100 or 9*3723, every number (at least that I've ever enountered) will always add up to a total of which is a multiple of 9. It's not always 9, but if your final number can't be divided by 9, you've gone wrong.
I think the worse issue is when kids can do 6*4 but struggle with 4*6, for example.
PJP2810@reddit
Not just ones you've encountered, this is a mathematical rule that is true for every number divisible by 9 (and the equivalent works for 3, the sum will always be divisible by 3).
One of the great parts is that because the rule applies to numbers divisible by 9, and the rule should leave you with a number divisible by 9, even for very large numbers, if you're not sure if the sum of the digits, you calculated is itself divisible by 9, you can just repeat the trick on that.
E.g. 1,178,250,624
1+1+7+8+2+5+0+6+2+4 = 36
If you didn't immediately recognise that 36 is itself divisible by 9, you can just do 3+6 = 9 and confirm it and this can be done infinitely until you get back to a single digit value which will be exactly 9 (for multiple of 3 it'll eventually hit either 3, 6 or 9)
Organic_Recipe_9459@reddit
Not only that up until you get 9x9, you’ve already done in the previous times tables.
Curious_Orange8592@reddit
No, I didn't learn it until I watched Stand and Deliver as part of a watchalong for the Unspooled podcast
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