Fast Math Tricks - How to multiply 2 digit numbers up to 100 - the fast way!

G'day and welcome to the TecMath channel. In this video today we are looking at the fast way of multiplying two two digit numbers together....so let's go! First of all we'll see if you can multiply some numbers together I'll give you a question which is twenty-one times thirty one. I'll give you six seconds to work that out. Go! So time's up. So if you got the answer of 651 you did really really well you got the right answer If you were busily reaching for the calculator but couldn't find it in time bad luck but you shouldn't need a calculator, and I'll show you how to work it out quickly Don't get all despondant if you didn't work it out I'll show you how to work these out So to get the first number of our answer we multiply the first digits in our two numbers here, so 2 x 3 is six, and we have the first part of our answer We leave a blank space. To get the last number of our answer we multiply the last digits of our two numbers here So 1 x 1 is 1. To get the middle part of this number here there is a bit of a trick. What we do is multiply this number and this number and this number and this number and we add the two answers together so 1 x 2 is 2 1 x 3 is 3 we add 2 and 3 together and get the answer six hundred fifty one Hey, pretty easy 'eh? We'll have a look at another one So, what about 43 times 21, a little bit harder this time See how you go. Have you got the answer yet? I'll start working through this one. So again 4 x 2 is 8 We leave the blank space 1 x 3 = 3 Then what we do is go... remember this.... 1 x 4, and we add this to 3 x 2 so 1 x 4 is 4 3 x 2 is 6 We add these together We get the answer of 10 Now this leads to a problem, so this is a little trick for to understand There is only one space here We only have space to fit one digit So the digit it puts in out of this ten is the zero, and for the one We carry this across And we add it on, so The answer we end up getting 1 + 8 is 9 0 3...nine hundred and three. Very good. I think we can go through one more I'll rub that out and let's have a look one more question I think this time I'll do it in a nice purple colour and I'll do the question here 42 times 63 I'm going all out, using different colours today, getting excited Too excited, I can't wait to get the answer - let's work it out First number 4 x6 Leave a space. is 24. Leave a space. 2 x 3 is 6 And then what we do And I hope not to get this wrong. I had to remake the video earlier as I stuffed up this one Occassionally I get all excited and I make mistakes too. But for YouTube videos we don't make mistake. We always get 100% correct OK OK We multiply These two guys together. 4 x 3 is 12 6 x 2 is 12 And 12 + 12 is 24. We add 24 on, OK? We put the 4 there and 2 there. So what answer did we get? Two thousan six hundred and forty six Hey that's the right answer. Pretty cool right? So if you practice these you will get really good at them and really fast. Your teacher will be utterly astounded about how good you are. Everyone will think your a genius alright? I mean don't go too far - people might stop talking to you but hey - you do this, you'll do really well. And yes you may make a few mistakes. We all make them. So finally I will leave you with a few questions I'll write them, get you to pause the video and work through them, then I'll work through the answers as quick as I can. Here they are. 22 times 34 I mean 32 see how you go on that one fifty-one times sixty three and 82 times fifty-one pause the video Then I'll get back to you A couple of seconds and we'll go through these. OK so hopefully you've worked through those and we'll go through the answers right now. OK so 2 x 3 is 6 We leave the blank space. 2 x 2 is 4 and then we add four and six together which is ten. We get the answer 704 The next one 5 x 6 is 30 Leave a space 1 x 3 is 3 and then we get the number 3 x 5 is 15, 1 x 6 is 6 15 plus 6 is 21, so I'll put that in a different colour so it fits This will be a one, and this will be a 2 so our answer is three thousand two hundred and thirteen On to the last one 5 x 8 is forty Leave a blank space 1 x 2 is 2 then we go 1 x 8 and we add that to 10 8 plus 10 is 18 - we put the 8 there and the one there. So our answer is four thousand one hundred and eighty two I hope you did well on those. See you next time

Channel: tecmath

Views: 8,156,706

Keywords: maths, tricks, for, fast, calculation, genius, math, speed, way, multiply, numbers, multiplication, teach, learn, Mathematics, Learning, calculate, vedic, homeschool, school

Id: PYrgjMubh-c

Length: 6min 26sec (386 seconds)

Published: Sat Nov 26 2011