How to Quickly Multiply Any Number Between 10 and 20 I The Great Courses

[@pavelsprojectfilms]

This method also works for doing numbers between 20-30, 30-40, etc. For example: 23x24 do 23+4 to get 27, but this time you have to double it because you're multiplying it by 20. So 27x20=540 plus 3x4 of the original problem, so 540+12=552

[@fbitm8089]

Wow

[@faizahmadpopal2079]

+George Belanger unfortunatly they don't

[@pavelsprojectfilms]

***** For 94 x 72, I'd do either 94 x 9 x 8 or add 6 to 94 to get 100 and do 72 x 100 then subtract 6 x 72. So, kinda have to play around with the numbers and see what you can do.

[@YashGumaste]

Thanks

[@hardmanhimselfss]

bro how you got that verified sign with only 7 subs

[@kanishmaray]

It's not just the methods (in fact, this is a very common method in my country) but the way he teaches... it feels so welcoming and weirdly interesting. If only my math teachers were like him *sigh*

[@prashantbokade347]

🤣🤣

[@anandhukumarp421]

i seriously doubt that..🤣

[@ben33584]

Professors like this guy should be allowed to CHANGE education. Oh i forgot the Educational Industry is the slowest to adapt to change meaning his methods will likely be used when he's no more in the next centuries. sighs!

[@erikk_]

agree!

[@uthirayinin6486]

Lesedi Ben boof

[@uthirayinin6486]

Monstf ong Kun

[@wealthmaster69]

So true

[@myyysgfftd]

Same in the uk education system I could have gone better

[@guddankumar973]

I saw this sir on Ted talk...

[@rishilkadakia4779]

Yes, same, he was on a Ted Talk called faster than a calculator Arthur Benjamin.

[@mathmadmedics8974]

Yes he’s the main person on Ted talk

[@saritapassi6988]

Me too

[@theaclones9345]

I know right. I was trying to find him after watching that video.

[@Chak_tak]

Same here

[@huh4801]

This man stole my strategy lol, I used this all the time in 3rd grade by breaking down the multiplication...Knew I was on to something

[@sarthakchavhan]

Lier lier aba

[@alyssapoynor2202]

I still use it in middle school, it's the easiest way to mentally solve a problem, and I always get the right answers the quickest lol

[@jab4634]

Quick call the math cops 😂😂

[@readjordan2257]

If thats the case, you shoulve went for a math degree. Math isnt about arithmetic often enough, but this playful attitude and being able to simplify, reform, or see between the instructions is a big part of successful mathematicians, amateur or professional.

[@ANTI_UTTP_FOR_REAL]

I'm still using that in 12th grade lol

[@szymong366]

I dont know why, but I always learn more from him, than I do from my math teacher. Keep up the great tutorials.

[@yuefang1030]

i love math so freaking much and this just made my multiplication life so much easier

[@TheGreatCourses]

We love hearing this and we're glad we could help, Yue Fang! Thanks for being a fan and never stop learning!

[@shanhmental]

Great Courses thanks Sir!!

[@Cosmic-hh9sw]

I didn't know this this will make multiplying a lot quicker

[@RYANFERNS19]

Oh yeah yeah

[@Risyn1]

I feel bad for the education system if you didn't know this yet

[@borisich88]

Loved it!! Your delivery is just beyond awesome! Thank you, sir

[@harshkathiriya439]

Another method for 13×14... 14(10+3)..... 14×10 + 14×3 140+42 182 Tricks for all is....convert into simplest number possible like number ending with 5 or 10

[@tonydauto822]

Saw this guy on Leo and Longevity's podcast and he's just an awesome dude, if I had a teacher like this I probably wouldn't have not cared so much.

[@lasseel3724]

Link?

[@CoolCat123450]

I always knew you could break down the multiplication, but when he says we can do it from left to right, it makes it mentally much easier for me.

[@montanacharles4154]

I just discovered this gentleman, phenomenal 😊

[@averdadeacimadetudo7612]

13 x 17 = (10 + 3) * (10 + 7) = 100 + 30 + 70 + 21 = easy right? Just get the two right digits in both numbers , multiply each by ten and add them up. Add 100 to the result and then add the multiplication of two right digits.

[@blitherithicus]

It seems doing a multiplication plus a subtraction is often more efficient. With, for example, 18 x 8, isn't using subtraction easier than using addition in combination with a multiple of 10? Multiply 20 x 8, which is 160, and subtract 2 x 8, 16, which yields 144. In the case of 19 x 7, 20 x 7 = 140, and subtracting one 7 = 133. (I wrote the first draft of this comment before noticing that a few seconds later the professor mentions this alternative method.) A good book to read from decades ago describing shortcuts in arithmetic is Isaac Asimov's Quick and Easy Math.

[@dnmextra62]

Blitherithicus that’s smart

[@VeerD]

This really helps me with my math homework! What an amazing strategy😇

[@dmitrijsk9037]

Homework? You're like 30 wtf

[@Jowzzz]

I did this and waw- my teacher impressed 😆

[@jimholmen7297]

Pavel Tarasov take 37 x 45. Add 37 + 5 and get 42. Multiply 42 by 30 because "37" has three groups of ten. 42 x 30 = 1260. Next step...the difference between 37 and 75 is four groups of ten so multiply the 37 by 40 and get 1480. Then multiply 7x5 and get 35. Add the 1260 + 1480 +35 and get 2775.

[@readjordan2257]

I remember watching this back when i had a great courses subscription

[@Alex1891]

Is there any reason it is recommended to add left to right?

[@TheGreatCourses]

Alex, to learn more about this subject, try our Free Trial of The Great Course Plus and watch Secrets of Mental Math here: www.thegreatcoursesplus.com/special-offer?US_OnlineVideo&SocialMediaEditorialKZbin&

[@MiKo-sr8wh]

fact that he had a hard time saying the answers because it was too easy for him.

[@wellcraft2136]

Not true. He was deliberately slowing so those watching could mentally calculate the answer for themselves. If such calculations were difficult for him there's no way he would be as successful a teacher as he is now.

[@sudan199156]

seriously amazing m enjoying mathematics....

[@Corazonlatino1995]

Another example is do 16×24 ~> they distance from BASE 20 are 4 so in my head quickly I will square 20² and subtract the square of 4 ~> 400-16= *384* ! Or about multiply 17×16 the distance of their number of BASE 10 is 7 and 6, so I will doing 17+6= *23.* and multiply 7×6= *.42* , so were 230+42= *272* . Or I will square 17² and subtract 1 times 17 ~> 289-17= *272* . The mental calculations are nice because we can use lot strategies to arrivals by the results, and every from us can apply the best of ourselves. 🤦‍♂️💪🤙

[@nicholastucci8951]

I love this Professor and I love the video even more

[@ПчелицаЏаја]

You sir, are breathtaking.

[@Corazonlatino1995]

Hi. For example another methid to do 17×15 is that I do the square of 16×16= *256* because 17 is 1 higher than not 16, and 15 is 1 smallest than not 16...... and at last I just subtract 1×1=1 from 256 and the multiplication about 17×15 will be = to 256-1= *255* !! I calculate it of BASE 16 as we had the BASE 100 to multiply for example 98×102 will be = to 100²-2²= *9996* , i done MINUS 2 because is the distance about 98-102 from 100. 💪🤙

[@alcoholicnerd514]

Hey, folks, was your webste banned in Russia or something? Can't get there without VPN

[@TheGreatCourses]

You're right, it's not currently viewable in Russia without a VPN.

[@alcoholicnerd514]

@@TheGreatCourses That's a pity! Was it the decision of our government or there are some technical issues?

[@nexpha2325]

your amazing at explaining now i can do it in my head

[@megha425]

omg! you solved my problem. thank you so so much for uploading this vedio :)

[@vasumathyb7997]

Thx professor!!!!!!!!!!!!!!! Thank you sir!!!!!!!!!!

[@keshavrajput6048]

the best video ever in my life

[@loln-word2146]

Keshav Rajput watch his ted talk video "faster than a calculator" that will become the best video ever

[@sidrao3984]

I just met this guy today

[@krishanuchatterjee1765]

Keshav vai India ka vedic math hai ye. Apna desh ko pehchano.

[@haideressa599]

awesome video I love numbers their are some easier method without momoriz it for example: 19*7=(20-1)(10-3)=200-60-10+3=200-70+3=133 13*14=(10+3)(10+4)=100+40++30+12=170+12=182 thats need you to be familier with numbers

[@IsaacLiz]

Underrated vids are better than popular

[@shajual1318]

You are a genius

[@bryandeleon8822]

I like your vids

[@aaweshkhali6317]

2020 is teaching me some great things

[@ManishKalauni]

They never teach this in school but if a person is required to do calculations multiple times then these methods will automatically come to the mind

[@omarperez671]

This guy is a genius, Wow why aren't they using this methods in schools

[@kwilson5832]

I'm not criticising Dr Benjamin's method, as I can see how it works and is much quicker than the 'traditional' method. But I guess that the reason that it isn't taught in school is because the method in this video only works if both numbers are between 10 and 20 (although other another comment in this thread does explain how it can be adapted to be used if both numbers are between 20 and 30, which can then be extrapolated to any calculation where the two numbers have the same leading digit). But this method won't work if the numbers have different leading digits eg 23 x 17. I'm sure Dr Benjamin has another method for such situations, but school students would then have another method to remember. The traditional method works whatever the two numbers are, so once the method has been learned, it can be applied to any calculation, even if it isn't as quick or as simple as another method that only works on pairs of numbers with certain properties.

[@theohaywood4199]

This video is so helpful.

[@moonlight-nz9cq]

Who noticed his tie was made out of symbols and numbers O.o (multiplication etc...)

[@sanjaydhiman9820]

you are damn right

[@alow33n]

He always wears that tie when doing math shows

[@mr.techrgu-thetechreader5515]

Amar Sir is more faster than him.

[@julians9070]

Delighted with how I can multiply numbers between 10 and 20. If this means relearn maths due to knowledge denied , I accept. No need for memory loss.

[@rgups07]

I found this useful for my son who has a test of multiplication up to 20 times table

[@saje1988]

How does this method work with 0. Like 20x15? Please help

[@TheGreatCourses]

Hi Saje, this method is for numbers between 10 and 20, so it is not applicable for numbers with a 0 on the end.

[@saje1988]

@@TheGreatCourses ok thanks

[@deeptadevkota5106]

Cant we add the numbers from right to left?

[@BrokenRecord-i7q]

Great sir!

[@alisharif4763]

You're tremendously fantastic, and great teacher, I hope to meet you, in the coming weeks. Thank you so much for your wonderful time, I appreciate your experience.

[@TheGreatCourses]

Hello Ali - Thank you so much for your kind feedback! We pride ourselves on having the best professors and are very glad you enjoyed this video. Thanks for being a fan!

[@waayoqofkaatahay7496]

Thank you boss

[@huidromchinglensana2623]

I also have another method Let's take 12x17, Here 12 X17 Multiply 2 and 7,we get 14 so keep 1 in hand and keep 4 as the last digit and add 12 and 7 , we get 19 and add 1( that keep in hand) ,we get 20. So the require no is 204

[@surendra_varma]

Thanks sir helps alot❤️

[@ENTERTAININGGAMECHANNEL]

AWESOME VIDEO😀😀😀😀

[@TheGreatCourses]

Thank you! We are glad you like it.

[@Doesit_matter]

Thanks prof 💕

[@saintpaulbetu7217]

Thank you Sir your method is very nice.

[@floralxriq]

this helped me so much

[@surubhabar7661]

Awesome... hope u were in every school in india... hates off... love u

[@menonfernando4932]

The startling video ever Professor thank you so much

[@OeilPhotography]

thank you Dr

[@tonychen5517]

theres also the criss cross way, which is reasonable for up to 3 digit numbers as well

[@mando5888]

Is Mathemagics still available online? My friend bought mathemagics last 1998 but someone stole it to him. I want to have a copy of mathemagics book. Hope it is available online thank you.

[@fatemehrahimi5779]

Thank you

[@kimchang6435]

I will you were my teacher you are like a math robot.

[@americanttm9889]

Thanks dude!

[@waltz9230]

How do you do it for 3 digit numbers?...

[@Aditya-im1uf]

Thank you sir, great job. I saw you in Ted Ed, ur are the human calculator🤓

[@The_pillars_24]

i realy like your way of explaning i had become your fan from india

[@abdurrouf6632]

thank you so much

[@prashantaggarwal6453]

Thanks sir..u are a pure Genius. .

[@rifathosan2455]

I am shook that a professor is teaching us this thing.

[@cuongluu1492]

Thank you for your teaching sir

[@gracielamyradelgado4469]

Great!!! Thank you😇😇😇

[@prdarkfirecaro5583]

If I had teachers like this when I was in school or college I would have been waaaay more interested in math.

[@btcdiamond.agario6478]

Nice bro your really smart and got good tricks

[@x-force7961]

What about numbers that involve a decimal point?

[@BhojpuriyaGangs]

I am from india,,,Thanks brother..

[@Parmenz]

Thank you!

[@mdude9211]

He should explain why these methods work.

[@Kai-bk4td]

this taught me better than my school

[@TheGreatCourses]

We are glad our lectures are being a good source of information for you, Antoinette! Thank you for your comment.

[@Football-oe1jn]

Thanks man

[@oscarrookie]

I love this guy! also he kinda reminds me of Jack McBryer lol

[@zephyrtrancome914]

Oh thank you so much i really did it in the book and got it I feel that I'm gonna do great in my exam and I feel very happy bty I'm 9years old😄💟💟💖💗

[@SrisailamNavuluri]

You are using distributive property 18×8=(10+8)8=80+64=144

[@muhammedkp5065]

It's Very very helpful.....I appreciate it....!!!!🤩😍😍😍😍

[@TheGreatCourses]

We are happt to hear your feedback! Thank you :)

[@vijaymisra8617]

Mathematics is an intresting subject unless we get fear....😃😃😘😘

[@annacacheiro9983]

Hi love you videos I figured out all the answers thank you for teaching this method🤗

[@crrgful]

Why add from left to right and not vice versa?

[@imkadosh]

I love this professor

[@TheGreatCourses]

Thank you for the feedback, Letitia! We

[@rahulvyas5485]

Dear, My name is Rahul vyas And i m nobody means m not Mathamagician or something I can make it more simple 14 x13 Always take one as one see in sequence 1,1=1 now see 4 & 3 Add them up 4+3=7 we got (17_) till now, then multiply 4*3=12 Now we are done add (17_) with 12, put 2 at the end and add 1 with seven = 182........simple I crack my own tricks But follow this man Mr.Benjamin He is G2 i mean Great=Guy.

[@jwhite973]

rahul vyas That's not more simple. That's pretty much exactly what he did in the video.

[@nobody3973]

I tried multiplying *14 x 15* and as I *added the results* from *left to right* it didn't worked, why?

[@rahuldhuriya273]

You are great sir

[@TheGreatCourses]

We are glad you liked this video, Rahul! Thank you for commenting.

[@うるる3517]

wow I wish I could attend his classes

[@dwhudhwhhjwdj]

Thankyou that helps so much

[@iliketheodds2575]

My idol.

[@mohamed-ii3th]

Top every clear and simple

[@waterlily1507]

Why do you have to go from left to right while adding

[@vinniejowell6076]

🎉 thank you so Mach

[@vinniejowell6076]

It’s help me a lot at math

[@wkekoekmkwk2k3jie35]

Awesome dude

[@salehabegum2692]

‘Tis guy is amazing

[@TheGreatCourses]

Thank you, Saleha!

[@victorgustavo4366]

great man. Hugs from Brasil

[@haeniielle182]

I saw this Amazing Guy on TedX

[@shawn980]

I figured out how this works. Take (x+3)(x+4) where x is 10 = x^2+3x+4x+12 = x(x+3+4)+12 = x((x+3)+4)+12, = 10((10+3)+4)+12 = (13+4)10+12.