Why does this trick work? And, what numbers does this trick work on? Does it work on 57 x 39? What about 352 x 148? In order for this trick to be useful, we have to know the range of numbers it will work on, so we don't apply it to incompatible pairs of numbers. Thank you.
It can be proved and generalized. (10 + a)*(10 +b) = 100 + 10(a + b) + ab = 10(10 + a + b) + ab ; if you think about it, that's exactly what we're doing here. If you're dealing with other digits it might be more convenient to simply switch the 10 in the equation for something else. For example, 57*39 = (30 + 27)*(30 + 9) = 30(30 + 27 + 9) + 27*9 = 30*66 + (10 + 17)(10-1) = 180 + 1800 + 10(17 - 1) - 17 = 1980 + 160 - 17 = 2140 - 17 = 2123. Of course here it kind of defeats the point if you have a faster method, but it does work. I wouldn't even try it on 352*148 though.
Thanks for the question. As said early in the video this works on teen numbers - numbers starting with ten. You may have missed that from my nasally accent.
@@tecmath Thanks. Yes, I heard you say that in the video (and for the record, I dig your nasally accent). But you also demonstrated the technique using a number not in the teens, so clearly it works for at least some other numbers. So I thought it might be useful for your viewers to know exactly which numbers this trick works for and which it doesn’t.
Thanks mate. I am a 67 year old Kiwi who left school at 14 but have always added oncoming number plates ever since I was a passenger as a kid and when I got my licence to drive I found I can also do that from the drivers seat so I have kept sharp with numbers. What I have learned through your vids over the years I now do to the young kids of the family sort of like a magician if you get my drift, LOL, it goes down a treat and I must seem like a MENSA member to them as it were. Little do they know that I am an uneducated dolt, albeit a happy Dolt-Hood. 😀
I'm in the UK, and we used to have three numbers on the registration plates when I was young. I used to try and get 11 (not sure why I chose 11) out of the three numbers by adding, dividing etc. Unfortunately, registrations around the turn of the century in the UK changed to having only two numerical characters, which spoiled all the fun, and means I can't teach my daughters to do similar to keep themselves sharp.
That is awesome! I do similar things. At the gym the other day it entered my head how many breaths a person takes in their lifetime and I try to work it out in my head. Really zens me out.
Good method, I like it. I generally multiply one number by ten, then add to that the number times the remainder. However, this way definitely makes for an easier sum. The biggest problem would be remembering to use this method, as I'm so used to doing it the other way.
That's the problem with this. Yes it's easy but younhave to apply a different rule as the numbers change.personally I'd do the method for all. 31*10 + 31*4 boom 534 .
ruclips.net/p/PLjbxBzUM6SLmzIG-wy_rKYZYNHdfg9V7P&si=YxK_LLi5T7xq3SWa
First?
🎉
If only my math teachers could have explained it as simply as this!
Thank you Josh for another multiplication refresher. You are encouraging many of us to stay and become increasingly numerate.
Thanks. I appreciate that.
I absolutely love your videos.....55 years old and finally learning math!
Glad to hear it! Gotta keep learning.
Why does this trick work?
And, what numbers does this trick work on? Does it work on 57 x 39? What about 352 x 148? In order for this trick to be useful, we have to know the range of numbers it will work on, so we don't apply it to incompatible pairs of numbers.
Thank you.
It can be proved and generalized.
(10 + a)*(10 +b) = 100 + 10(a + b) + ab = 10(10 + a + b) + ab ; if you think about it, that's exactly what we're doing here. If you're dealing with other digits it might be more convenient to simply switch the 10 in the equation for something else. For example, 57*39 = (30 + 27)*(30 + 9) = 30(30 + 27 + 9) + 27*9 = 30*66 + (10 + 17)(10-1) = 180 + 1800 + 10(17 - 1) - 17 = 1980 + 160 - 17 = 2140 - 17 = 2123. Of course here it kind of defeats the point if you have a faster method, but it does work. I wouldn't even try it on 352*148 though.
Thanks for the question.
As said early in the video this works on teen numbers - numbers starting with ten.
You may have missed that from my nasally accent.
@@tecmath Thanks. Yes, I heard you say that in the video (and for the record, I dig your nasally accent). But you also demonstrated the technique using a number not in the teens, so clearly it works for at least some other numbers. So I thought it might be useful for your viewers to know exactly which numbers this trick works for and which it doesn’t.
@@isferis This is excellent and really helpful. Thank you!
@@rc2257 much appreciated ! Have a nice learning journey
Thanks mate. I am a 67 year old Kiwi who left school at 14 but have always added oncoming number plates ever since I was a passenger as a kid and when I got my licence to drive I found I can also do that from the drivers seat so I have kept sharp with numbers. What I have learned through your vids over the years I now do to the young kids of the family sort of like a magician if you get my drift, LOL, it goes down a treat and I must seem like a MENSA member to them as it were. Little do they know that I am an uneducated dolt, albeit a happy Dolt-Hood. 😀
I'm in the UK, and we used to have three numbers on the registration plates when I was young. I used to try and get 11 (not sure why I chose 11) out of the three numbers by adding, dividing etc. Unfortunately, registrations around the turn of the century in the UK changed to having only two numerical characters, which spoiled all the fun, and means I can't teach my daughters to do similar to keep themselves sharp.
That is awesome!
I do similar things. At the gym the other day it entered my head how many breaths a person takes in their lifetime and I try to work it out in my head. Really zens me out.
I’m not that bright in my multiplication and my teacher wants us to be able to mentally multiply..! Thanks for the video, pal :]
Thanks! Im loving your videos! Helping me get quicker for my SAT
Good method, I like it. I generally multiply one number by ten, then add to that the number times the remainder. However, this way definitely makes for an easier sum. The biggest problem would be remembering to use this method, as I'm so used to doing it the other way.
Thanks for sharing!
This seems like a silly question but what program do you write in? It looks really smooth.
So what do you do if you move on to say 31 x 14? Ur videos are great by the way.
For that - I'd use a different method... Coming up.
That's the problem with this. Yes it's easy but younhave to apply a different rule as the numbers change.personally I'd do the method for all. 31*10 + 31*4 boom 534 .
@@shadesofgray9434
I wish you were my maths teacher when I was a kid…I would have learnt so much more!
Thank you.
Im i stupid but guys please try this 13 x 15 = ?
Awesome 😎
Thanks 🤗
not always working. says 17 x 23?
in your computation it will be 300 + 21 = 321
17 X 23 (units 7 and 13)
300 + (7 x 13)
= 300 + 91
= 391
Thank you! I’m a reading tutor but we do math sometimes too. Do you know about Singapore math?
Thanks. What is Singapore math?
You are really the best.
Thank you for your great teachings.
I had a difficult exam in a few days and my problem was solved with your videos.🙏🏻
238
Best teacher ever I’m a 12 year old understanding year 12 math.😂
Upload videos regularly or your channel will dead but i am a big fan of your channel
Thank you so much I wish the last guys have understood 🎉❤
It works only if the first digit of the second multiplier is 1.
By example 21 x 24 ?
The method will not work.
As said in the video.
Different methods should be used for this one.
Lemme try 354
Yeah jt didn't work.
@@rizzwan-42069it does work in this case.
@@RichAbe23 where did i fumble
So fast, 2 seconds. 1001, 1002 done.
This is vedic maths