Placeholder Image

字幕列表 影片播放

  • 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

  • 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

G'day and welcome to the TecMath channel. In this video today we are looking at the fast

字幕與單字

影片操作 你可以在這邊進行「影片」的調整,以及「字幕」的顯示

A2 初級

數學秘技 (Fast Math Tricks)

  • 196 23
    Bill Yu 發佈於 2013 年 05 月 01 日
影片單字