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• 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

A2 初級

# 數學秘技 (Fast Math Tricks)

• 196 23
Bill Yu 發佈於 2013 年 05 月 01 日