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超快速计算100以内两个任意数乘法

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 multiplysome 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 651you did really really well you got the right answer

If you were busily reaching for the calculator butcouldn’t find it in time bad luck

but you shouldn’t need a calculator, andI’ll show you how to work it out quickly

Don’t get all despondant if you didn’t work it outI’ll show you how to work these out

So to get the first number of our answer wemultiply the first

digits in our two numbers here, so2 x 3

is six, and we have the first part ofour answer

We leave a blank space.

To get the last number of our answer we multiply the last digits of our two numbers hereSo 1 x 1 is 1.

To get the middle part of this number here there isa bit of a trick. What we do

is multiply this number and this number and this number and this numberand we add the two answers together

so 1 x 2 is 21 x 3 is 3
2和3相加 结果就是651
we add 2 and 3 togetherand get the answer six hundred fifty one

Hey, pretty easy ‘eh?

We’ll have a look at another one
43×21呢

times 21, a little bitharder 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
1×3＝3 然后
1 x 3 = 3 Then what we do is go…

remember this….
1×4和3×2 两者相加 1×4＝4
1 x 4, and we add this to 3 x 2so 1 x 4 is 4
3×2＝6 和是10
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 hereWe 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 differentcolours today, getting excited

Too excited, I can’t wait to get theanswer – let’s work it out

First number 4 x6Leave a space.

is 24.Leave a space.
2×3＝6 下一步
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 makemistakes 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
6×2＝12 12+12＝24 在这里填24对吗?
6 x 2 is 12 And 12 + 12 is 24.We add 24 on, OK?

We put the 4 there and2 there.

So what answer did we get?
2646
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 andreally fast. Your teacher will be

utterly astounded about how goodyou are. Everyone will think

I mean don’t go too far – peoplemight stop talking to you but hey –

you do this, you’ll doreally well.

And yes you may make a few mistakes.We all make them.

So finally I will leave youwith a few questions

I’ll write them, get you to pause the videoand work through them, then I’ll work through

the answers as quick as I can.Here they are.
22乘34 下一题 55乘63
22 times 34 I mean 32 see how you go on that one fifty-one times
82乘51
sixty three and 82

times fifty-one pause the video

Then I’ll get back to you

A couple of seconds and we’llgo through these.

OK so hopefully you’ve workedthrough those and we’ll go through the

OK so
2×3＝6
2 x 3 is 6

We leave the blank space.2 x 2 is 4 and then we add four
4+6＝10
and six together

which is ten. We get the answer704

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+6＝21 换个颜色
15 plus 6 is 21, so I’ll put that in a differentcolour so it fits

This will be a one, andthis will be a 2 so our answer is three thousand

two hundred and thirteen On to the last one
5×8＝40 空一格 1×2＝2
5 x 8 is forty Leave a blank space 1 x 2 is 2

then we go 1 x 8 and we add thatto 10 8 plus 10
8填在这 1在这
is 18 – we put the 8 there andthe one there.

4182
one hundred and eighty two

I hope you did well on those.See you next time

survivor

SC