Mental multiplication in 3 seconds

Want to knowhow to multiply some big numbers almost instantly in your head?
This trick is a great addition to add to your mental math toolbox.
Here is THE mental multiplication lesson playlist - progressing you through your mental multiplication.
• Tecmath's mental multi...
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[@stevecampos1960]

My 7th grade math teacher taught me the trick for the square of numbers ending in 5, which I had opportunity to use on various occasions, including on my SATs, but I had not known about the trick for the other complementary numbers until today.(almost 50 years later). Better late than never. Thanks!

[@paysour1]

He'll know I'm mad as hell. 50 years later I am pissed this guy wasn't my math teacher.

[@davidlewis1680]

You know I love dipping my toe into your lessons . I have to say though I think I have a fear of maths every time I look at your lessons my heartbeat goes crazy.

[@nano34677]

good lord lessons dont have tongues

[@riggsron]

I'm an old guy with memory issues. These tricks of yours are excellent exercises for me. Greatly appreciated.

[@wesmatron]

That doesn't make sense... You could forget the trick, surely? I'm not trying to be a smart-arse.

[@riggsron]

@@wesmatron oh I certainly do. But I still keep trying anyway sometimes lasts for a few minutes to hours. It's not like Alzheimers where you don't have good days. I do.

[@macslifestyle3763]

Mmmmmmmmm

[@HipsterDoofus100]

Dude you posted this 8 times

[@cheongyei]

Excellent trick...rare set of circumstances allow it, but great when the tens digits match and the ones digits add to ten. Thanks for sharing all you share.

[@SpaceWithSam]

Excellent content! Such a great explanation! Great work sir!

[@liamoreilly308]

Awesome way to work out multiplication of big numbers, wish we were taught this method at school and I would have enjoyed maths so much more, thankyou !

[@zerotoleranceforsataniceli4794]

Hi there! I didn't get your way easily & would struggle to remember the rule But this is an older way of doing it & feels easier to remember, as you just round the big numbers up on one side & down on other side to nearest even number & so make them simpler to multiply in the tens & hundreds column & then just multiply the units as done in video . 63 x67 = 4221 same as 60 x 70 =4200 plus 3x7 =21 Total 4221 21 x 29 = 609 same as 20 x 30 = 600 plus 1x9 =9 Total 609 114 x 116 = 13,224 same as 110 x 120 = 13,200 plus 4 x 6 = 24 Total = 13,224 etc 45 to power of 2 45 x 45 = 2025 same as 40 x 50 = 2000 plus 5 x 5 = 25 Total = 2025

[@zerotoleranceforsataniceli4794]

@John Wright Mmm... I didn't know that one, but it involves remembering a rule! & in certain situations only! I look at it with the least work to do, so, 35 to power of 2 is 35 x 35 = 1,225 or 30 x 40 = 1,200 plus 5 x5 = 25 Total = 1,225 I'm just borrowing from one figure & adding that amount to the other, so as to make the numbers simpler & so I can do it in my head. It is a rule of sorts and it works for simple stuff, but it doesn't really involve remembering. It's more of problem solving! In fact, it works for long complicated numbers too, but then it's not quick as you break it down into a collection of numbers which must then be added together etc

[@agasthya1747]

@@zerotoleranceforsataniceli4794 what's 14x14

[@zerotoleranceforsataniceli4794]

@@agasthya1747 👍👏😉 My way works for difficult figures that need to be simplified in your head, but it's not a rule as such. Your 14 x 14 are simple figures that don't benefit from further simplification as you can see! However, I had a go & I can make it as 12 x 16 = 192 + 2 from 6 = 4 ( why? 'cos I'm down 4 & must find it !!) Total = 196 or 13 x 15 = 195 but I've no idea where or how to get an extra 1 ! to make 196 This is simply playing! Personally, I would just do long multiplication the old fashion way as the figures are simple enough to work with. ( can't remember the rule explained in the video.)

[@zerotoleranceforsataniceli4794]

@@agasthya1747 Ps I'm not thinking straight today !! Ignore my last reply! 14 x 14 = 196 or 10 x 14 = 140 + 4 x 14 = 56 or break down the 4 x 14 to 4 x 10 = 40 + 4 x 4 = 16 Total 56 so 140 + 56 = 196 This worked by only simplifying the left side and leaving the right side alone.

[@douglasnewman4163]

Love this channel! I love learning new things at my age.

[@johnwarren2095]

Excellent‼️ Every little bit helps. 🤙🏽

[@wilfdarr]

“before you blast away in the comments...” No no no, that's what drives the algorithm!😁

[@BigHat83]

Plot twist, that's what he wants... That's why he keeps suggesting it

[@AbuelitaAlyssaAnn]

I enjoy your content. I really had fun this trick. I’m going to show my children. Thank you for sharing! 💗

[@debottamsarkar7684]

Wow what a great maths teaching . I have got full marks in maths for this teaching 😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮😮.

[@Diya-hu5yk]

Oh! 😮God this trick is super amazing thank you so much for this.

[@tipsybass7060]

What a great trick! In the 80s/90s, at least in my classes, we were drilled daily on our multiplication tables

[@ytsux9259]

This trick works but it's useless because 99.9999999999999999% of the time, you won't run into a multiplication problem with those requirements (first digits are the same and last digits add up to 10). LOL!

[@baldeagle7604]

@@ytsux9259 bingo.

[@gwiyomikim5988]

Hmm...is it easier to remember these “tricks” or remember where I put my calculator.🤔

[@alekku1782]

Tricks b1tch....bro teacher wont let us use calc..

[@lizzybach4254]

Well... Many exams don't allow calculators.

[@PrinceBieBrockP]

💀💀💀

[@ILOVEMYCATZZZ]

The tricks

[@jellytrooperjeff8034]

@@ILOVEMYCATZZZcap

[@242math]

very neat trick, this is so useful

[@MSUSPARTANS1973]

I love this channel!

[@RandomJ2023]

Me: bored KZbin: Want to learn some cool math from Bruce in Finding nemo? Me: Sure, why not.

[@beckitibaldi9654]

Cool! Love when you teach mental math bits like this.🙂

[@sydneydrake2789]

i love that trick. thank you

[@carol76543]

Wow! Thank you so much!

[@rhkiewalters1150]

Very much appreciated. Thanks

[@somakiran3263]

I know this way before but thanks for making a video and a new subscriber here

[@claythomas6587]

Thanks for the tool!

[@1001MathTricks]

Great work👍

[@tagordon6678]

Awesome job!

[@lauramariawaugh5719]

Thanks that’s a good one. I really like how fast we get the squared answer.

[@marcobuitrago1071]

You mean the squares ( of 5) not square root. That's totally the opposite

[@flywithaly]

Thank you so much

[@codecontent]

That's amazing!

[@iaminorinloverchannel422]

Thanks

[@firozahossen8307]

Great teaching very well explained thank you for sharing stay blessed

[@PINACI]

Probably easier to stick to the method you find best works for you for all multiplications. My preferred method is Vedic which works for any sum rather than trying to remember multiple methods. But you are my favorite math teacher and have helped me help my son over the past two years.

[@anoshgaming9924]

I living in India am learning western math And this guy is teaching me vedic math

[@anoshgaming9924]

Ironic

[@deviationblue]

I wasted thirty-odd years learning western maths and being horrible at it. Vedic maths are superior in every way for everyday calculations.

[@robinbowman1880]

Outrageously interesting... thank you

[@darinmustafa6615]

You made my day thanks in school it's too hard but u made it easier

[@roxanna910]

Dang, had been my math teacher, I would have been that physicist. Thank you for sharing your math tips :))

[@pearlwhite3009]

This is great!

[@oldpcgaming542]

0:11 "I am gonna give you 3 seconds." Actually gives us 6 instead of 3. Imagine if the teacher did the same during the examinations.

[@tecmath]

Hey what can i say? I'm a nice guy! The big question...did you get it in 6 seconds?

[@shubham3452]

I was watching in 2x :)

[@_ABHITIWARI]

@@tecmath 🤣

[@oldpcgaming542]

@@tecmath Sadly, I was not fortunate enough to know this trick at the time of my examinations.

[@OGTrueX]

@@oldpcgaming542 same

[@cars4170]

Superb man. You're great. Mind-blowing explanation. I mean how do you do this ?

[@texangrammy]

Thank you!!!!

[@bathshebabethsaidaleroux9321]

Wow thank you

[@rosario80340]

Thx its amazing... am glad to play tricks on math... its helpfull to teach my kids... am ur subz... thx

[@ricky18redblack31]

May be practical, but works like a charm. Thank you.

[@marygagliardi5315]

Fabulous!

[@tiajasminethet9055]

Love this!!! Helps me so much

[@iaminorinloverchannel422]

Thanks

[@tecmath]

Glad to hear. Thank you for watching.

[@tommcgee9631]

I love being able to use tricks to do basic math faster than most people can type it into a calculator. I’m definitely going to practice this one more and add it to my mental box of tricks. Great job.

[@KKMaths777]

Good way of teaching

[@jyotichandekar9936]

That's amazing 😻😀👍

[@tonybarfridge4369]

Yes that squaring trick I worked out for myself previously tho I'm only average at math. For a number ending in 5 like 75, multiply the tens digit 7 by the next 8, =56 then put 25 (5^2) after it. Simple as that. For 12^2 if u don't know tables above it, u can do 12^2+12 (12x13) or 156. It's good to learn squares up to 20 at least or higher if possible. The principle is similar as shown with 2 numbers the tens digits are the same and the unit numbers add to 10. Like 63x67. 6x7=42, the units 3x7=21, so 4221

[@shelettejohnson3836]

Amazing

[@axay5766]

Tfs, great tips 👍👍👍

[@shelley9263]

I guessed 3621 in a few seconds. I was wrong, but close.

[@mjdedge3440]

I try round one the numbers up or down to the nearest 10 and adjust after that. E.g. For 21 x 29; I do 21 x 30 = 630, then deduct 21 = 609 Or Sometimes I break it into 2 simpler calcs, E.g. For 21 x 29; I do 20 x 29 = 580, then 1 x 29 = 29; Then add the 2 = 609

[@hehf1828]

I think that's what most people do

[@abigailguzman2492]

Thanks

[@aletaschulz1108]

More please🤗💚

[@dr.jamesolack8504]

I’m pushing 70 and I think these tricks are great! However, the one drawback is that the student doesn’t really understand WHY they’re arriving at the answer. That’s where doing the long version explains HOW you arrive at the answer. For instance, why do you multiply the 10s unit by 7? Saying that you increase the 10s place by 1 then multiply the 2 numbers needs further explanation. Do you get what I’m saying? When you’re first learning math, you need to understand the WHY and the HOW of the computation.

[@kittyjohnstone5915]

Dr James Olack, you are so on the mark with your comment; without understanding of what is happening, it is so easy to misunderstand other processes which depend on the working knowledge gained by learning the long version. But, yes, the tricks are fun. Possibly much more fun when the underlying is understood first.

[@WeLuv9x5]

It’s a great supplement to re-learn basic multiplication.

[@Jagosix]

@mike bee If you don't resolve the issue of what's causing the problem, it will constantly be a issue not fixed. Hence why so many things IN THE REAL WORLD are messed up (unresolved). People want quick fixes with no real solution to the problems.

[@chrisbowring4298]

@@Jagosix 💯👍 ....much as in life... oftentimes it's not so much the destination as it is the journey. 😉

[@AbuelitaAlyssaAnn]

Obviously this “trick” which is actually “mental math”, is not meant for everyone, especially not for students just beginning multiplication. Once a math skill is introduced, understood practiced, etc, then mental math can sometimes be implemented as well. Many math departments strongly encourage and support incorporating mental math skills into the lessons. Enjoy today everyone! 💗🌞💗

[@kamarakoon3132]

Thank uuuu❤

[@Friendroid]

The older I get, the dumber I feel.

[@Dazzzb]

Me to🤔

[@nerdypunkin4336]

Not your fault schools didnt teach us the way

[@douglasnewman4163]

We were just never taught this way. Makes me wonder why not?

[@fjb4932]

Friendroid, A dumb person feels wise, while a wise person feels dumb. ...

[@brianping3105]

the older I get, the rounder I feel (and am, lol..)

[@Steve-qt9ce]

Cool!

[@kbisulca]

I use this for any squares ending in 5!!

[@ALternaprof]

It works because if b+c = 10, then (10a + b)*(10a + c) = 100a(a+1) + bc.

[@karhukivi]

Excellent! Your comment is better than the video!

[@ALternaprof]

@@karhukivi Thank you for noticing!

[@loophole9973]

Cool trick! Do you have a trick that works with any number? Thanks!

[@cathlenetraverns2294]

Yeah, 👍👍 Brilliant😄😃

[@beverleypeacock]

Cool...Sweet

[@IbrahimMohamed-zj3dr]

Is so helpful 😘😘😘

[@rfcasey]

Love these tricks. Do you know the X 5 trick. Any number multiplied by 5 is the same dividing that number by 2 moved over one decimal place to the right. ie 5 x 10 is the same as 10/2=5 move over 1 decimal place to the right and your answer is 50. Another example 5 x 625 is same as 625/2=312.5 move 1 decimal place over to the right, and your answer is 3125. Keep these tricks coming

[@theolivebeanissus3425]

IT WORKS!!!

[@OoiPaul]

When do you find a scenario in your life meeting the two conditions, same first number, the two second numbers add up to ten. Interesting though.

[@karhukivi]

Yes, when its 36x33 we will really feel cheated!

[@kerrynight3271]

Any time you need to square a number ending in five.

[@marcobuitrago1071]

@@karhukivi not really! Let me show you how: 36x33 Add 36+3=39 (because they are the same base, we can add the tenths numbers, 6+3 and keep the base 3 at the same time) now, remember it is base 30 Meaning, x3 39x3=117 keep that aside, Finally, multiply the single digits: 6x3=18 but be careful, the 18 has 2 digits, only the 8 can go there. The 1 gets carried over the 7 in 117 meaning 7+1=8 Final answer:1,188

[@karhukivi]

@@marcobuitrago1071 I would do that by long multiplication quicker! But anyway, who needs to do such calculations without a calculator?

[@markdaniel8740]

Like he said at the end. It doesn't always apply, it is just another trick. My boss constantly calls me with a few numbers and asking "how many cubic yards of concrete" or "how many tons of dirt". I am almost always able to find a trick that works or if not, I can cheat to a good approximation. 63x68 doesn't work for this trick, but it is 63 more than 63x67 or 68 more than 62x68. It might add a couple of seconds though.

[@kris4362]

Cool 4 cats mate .............. 👍👍👍👍👍👍👍👍😎 (Hokitika Sth Westland NZ)

[@MrSpidey1970]

Nice

[@philobeddoe8342]

So this allows you to look like 'Rainman' in certain instances.

[@jonathant.powell7281]

WOW! 😁

[@neilb1334]

I wish I knew this when I was in school.

[@teresamcgauley7441]

I thought I was good at maths but apparently not although I got the first one ☝️ I thought Martha would be interested in this..Apparently in the comments one says it is an old method, but it must be ancient as I have never heard of it before I hope that this will help Martha Love 💗 Granny T xxxxxx

[@1trucxhondamov589]

63x67 makes me think! 😃

[@petecastle5762]

Cool

[@kokanee2010a]

a squared plus b squared plus 2ab 37 x3 = 111 , 37 x 12 = 444 , 37 x 27 = 999

[@awickedtribe]

I am so number dyslexic that I tried this 30 times using the equations presented here... But every time I get the same answer 63 x 67 = Colorado...

[@Jagosix]

william white - If you need help understand math and the way numbers work. Let me know. As long as you can do the basic math + - / * with single digit, the sky's the limit.

[@Jewel22268]

Yes ingenious- but I see why it wasn’t taught- brings confusion -must have a valid technique that works every time!

[@ytsux9259]

Cuz this trick is useless in 99.999999999999999999999999999999999% of the time.

[@rightfullyron9365]

What??? School would been that much easier had I had that trick. up my sleeve. My trick was the calculator.

[@johnchestnut5340]

When practical I prefer more generally applicable "tricks". But it's not bad. You just have to remember when it can be applied.

[@bigcatfish5029]

ONLY TAKES A FEW SECONDS TO DO IT LONG MULTIPLACATION

[@dorothyjohn6418]

Like it

[@itzblue0]

yeyyyyy

[@wnJhntn]

The trick is a bit situational but its good

[@bathshebabethsaidaleroux9321]

I need more time and help to learn this.

[@rogergreen9861]

Guy at a bar: Hey, wanna see a cool trick? Woman he's just met: Sure Guy: Give me two numbers but make sure they have the same multiple of 10 and the lesser integers also add up to 10 Woman: *vanishes* Guy: ta-daaaa

[@nicolechan4474]

Thank you for this laugh. 😆

[@tiajasminethet9055]

Can you do a year 6 one? Like a playlist of things for year 6

[@iaminorinloverchannel422]

I'll try

[@MSUSPARTANS1973]

Hi! Are you asking him to make a playlist of all his videos that would be appropriate for a kid who’s 6-years old, or a kid in the 6th grade? I don’t mean to be harsh, but either way, you’re asking way too much. He’s not your child’s personal tutor. As a math teacher, if your kid is 6, he or she is probably a bit too young for this channel. If your child is in grade 6, simply scroll through his videos and pick out what you want. You can also search his name and the concept, for example: techmath- percentages. And all his videos on that topic will come up.

[@finhz]

@@MSUSPARTANS1973 this. I agree with this.

[@eddy2fast534]

3×9=27 = 3- 1=2+7=9 =2&7 =27 : 4x9=36 = 4 - 1=3 +6 =9 =3&6=36 Minus 1 from the first digit then add a number to make 9. When I worked this out on my own I thought why the HELL didn't they teach me this at school. Same with your method. Now I know school is to designed to keep us dumbed down.

[@davidarndt4699]

This trick works, granted, but, I am "Dyscalculic". Meaning, I have a learning disorder called: "Dyscalculia". This is a Math learning disability. I've attempted Algebra I twice. I had to drop the class twice, because I was in danger of failing it! This may make Math easier, but, it still confuses me. Just doing basic Addition, Subtraction, Multiplication and Division are hard for me. I still can't figure these problems out in 3 seconds! It still will take me an hour just to figure out the answer to 1+1! Every time I figure out a Math problem in my head, I type it into a calculator and I get a different answer! I go with the answer the calculator gave me.

[@Jagosix]

David Arndt - Wow... sorry you're having such a hard time with math. Everything in life is based on numbers. We all just see it in a different way. You just need to find a method that relates to your way of understanding. I can help you with that, IF you want it.

[@lovelycarpio1730]

Can i have the different conditions pls? Tnx

[@charleshenderson6890]

3 second class. 15 minutes of work.

[@patricka.crawley6572]

Don't cross-out the 7s. There's nothing wrong with them.

[@dr.jamesolack8504]

Good one!! I never understood that European 7. I suppose to differentiate between a 1 maybe?

[@patsmith5947]

That drives me crazy too, I never understood why some people do that, a 7 doesn’t look like a 1 at all.

[@henriknielsen1176]

@@patsmith5947 There's probably a lot you don't understand.

[@luzleal-esqueda5144]

Love math for breakfast

[@hoseamatavao1483]

👍

[@ironsights1809]

Good trick. I'll stick to my calculator.

[@BryBry2ply]

I was struggling with 6x7

[@leehunter1967]

🙏✝️

[@ksportz66]

The first condition…. Check this only works in 14 * 14 cases if the Left digit is on your left hand a a calculator is allowed in Bendigo.

[@ksportz66]

Sorry I ranted before you saying it is limited…. The 45 squared is pretty usefull though as it is my age in 2025 and I was born 45 years ago so 452025 is my ATM PIN.

[@abiodunaghedo550]

Trick for multiplying things like 12 × 40 = 120 × 4

[@aclemasultan1794]

I can easily use that trick in just 2 seconds.

[@aclemasultan1794]

Also i can square any 2 digit numbers that end in 5 lightning fast.