How to Quickly Multiply Any Number Between 10 and 20 I The Great Courses
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- Опубліковано 7 вер 2024
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If you know your multiplication tables up to 10, you already know your multiplication tables up to 20-you just haven't realized it yet. In less than five minutes, you can unlock the simple math tricks to put together dozens of two-digit multiplication problems in no time flat. Reach into your top hat and pull out some mathemagic.
Presented by Arthur Benjamin
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#MathTricks #Multiplication #Mathemagician
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
Wow
+George Belanger unfortunatly they don't
***** 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.
Thanks
bro how you got that verified sign with only 7 subs
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*
🤣🤣
i seriously doubt that..🤣
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!
agree!
Lesedi Ben boof
Monstf
ong Kun
So true
Same in the uk education system I could have gone better
I saw this sir on Ted talk...
Yes, same, he was on a Ted Talk called faster than a calculator Arthur Benjamin.
Yes he’s the main person on Ted talk
Me too
I know right. I was trying to find him after watching that video.
Same here
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
Lier lier aba
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
Quick call the math cops 😂😂
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.
I'm still using that in 12th grade lol
i love math so freaking much and this just made my multiplication life so much easier
We love hearing this and we're glad we could help, Yue Fang! Thanks for being a fan and never stop learning!
I dont know why, but I always learn more from him, than I do from my math teacher. Keep up the great tutorials.
Great Courses thanks Sir!!
I didn't know this this will make multiplying a lot quicker
Oh yeah yeah
I feel bad for the education system if you didn't know this yet
Loved it!! Your delivery is just beyond awesome! Thank you, sir
I just discovered this gentleman, phenomenal 😊
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.
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.
Link?
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.
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
fact that he had a hard time saying the answers because it was too easy for him.
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.
Thx professor!!!!!!!!!!!!!!! Thank you sir!!!!!!!!!!
seriously amazing m enjoying mathematics....
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.
I remember watching this back when i had a great courses subscription
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. 🤦♂️💪🤙
This really helps me with my math homework! What an amazing strategy😇
Homework? You're like 30 wtf
I love this Professor and I love the video even more
omg! you solved my problem. thank you so so much for uploading this vedio :)
Who noticed his tie was made out of symbols and numbers O.o (multiplication etc...)
you are damn right
He always wears that tie when doing math shows
Amar Sir is more faster than him.
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.
Blitherithicus that’s smart
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. 💪🤙
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.
You are a genius
I did this and waw- my teacher impressed 😆
the best video ever in my life
Keshav Rajput watch his ted talk video "faster than a calculator" that will become the best video ever
I just met this guy today
Keshav vai India ka vedic math hai ye. Apna desh ko pehchano.
I love this guy! also he kinda reminds me of Jack McBryer lol
Underrated vids are better than popular
thank you Dr
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
Thank you boss
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
This video is so helpful.
The startling video ever Professor thank you so much
Thank you very much
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.
AWESOME VIDEO😀😀😀😀
Thank you! We are glad you like it.
2020 is teaching me some great things
Great sir!
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
You are using distributive property
18×8=(10+8)8=80+64=144
your amazing at explaining now i can do it in my head
You sir, are breathtaking.
Thanks prof 💕
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😄💟💟💖💗
This guy is a genius, Wow why aren't they using this methods in schools
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.
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.
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!
I found this useful for my son who has a test of multiplication up to 20 times table
this helped me so much
I will you were my teacher you are like a math robot.
Thank you sir, great job. I saw you in Ted Ed, ur are the human calculator🤓
My idol.
If I had teachers like this when I was in school or college I would have been waaaay more interested in math.
I have another idea:
For example 13x14 is 13x15 that is really easy to calculate because 13x10 is 130 and 13x20=130x2=260 and 13x15 Is 195-13=182
Darius Popa Lol
Apj People 1000 IQ intensifies
Get another idea itzz too slow
When I was in elementary they forced is to memorize they forced us to memorize all the way up to 12x12. I went out of my way to memorize all the way up to 18x18. Man I wasted my time.
Yeah, I'm still in Elementary and they expect us to memorize the tables by ourselves without their help and assistance. And they'd also expect us to remember the stuff we learned YEARS ago, it could just be my weak memory but during those years my mind has been filled with new things in maths and I can't remember exactly the stuff I learned back then, or the words that we saw in the book like Perimeter, Index rotation etc.
Thanks man
i realy like your way of explaning i had become your fan from india
Thank you
theres also the criss cross way, which is reasonable for up to 3 digit numbers as well
He should explain why these methods work.
Awesome... hope u were in every school in india... hates off... love u
I am from india,,,Thanks brother..
Thank you Sir your method is very nice.
I like your vids
Top every clear and simple
Thanks sir helps alot❤️
Sir u r gr8
Thanks sir..u are a pure Genius. .
Thank you!
13*14=13*13+13=169+13=182.
15*17= 16*16-1= 255.
Thank you for your teaching sir
Pretty good
Nice sir
Hi love you videos I figured out all the answers thank you for teaching this method🤗
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.
rahul vyas
That's not more simple. That's pretty much exactly what he did in the video.
Is there any reason it is recommended to add left to right?
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&SocialMediaEditorialUA-cam&
The easiest way to solve
13
x14 and other numbers. Is by multiplying 3*4=12 then add 3+4 = 7 +1 from 12 = 8 then multiplying the tenths.. 1*1=1.. Ans. 182.. Trust me this is very easy when you just think of it.
Not clear. Pls explain with 16×17
@@anujchhabra3660 if doulble digit is the result of multiplication which is 42, just add the tenths to the next step. If would be 17 then do the same thing with the last step.. Would be 2*1. Answer 272.. Hope it helps
this taught me better than my school
We are glad our lectures are being a good source of information for you, Antoinette! Thank you for your comment.
Mathematics is an intresting subject unless we get fear....😃😃😘😘
You are very sweet and intelligent Sir......😊😊😊😊
Nice bro your really smart and got good tricks
Thanks dude!
Thankyou that helps so much
Super!
Wu Tang!!! Collllllddd blooded!
Nice tie
Thank yous so much
great man. Hugs from Brasil
I am shook that a professor is teaching us this thing.
‘Tis guy is amazing
Thank you, Saleha!
Awesome dude
I love this professor
Thank you for the feedback, Letitia! We
I'm gonna move my index finger and sub to this channel
Great!!! Thank you😇😇😇
Thank you for helping my question in math