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

大家好 欢迎来到数学教育频道 本视频我们讲解
G’day and welcome to the TecMath channel.In this video today we are looking at the fast
两个任意数相乘的速算法 下面开始
way of multiplying two two digit numbers together….so let’s go!
首先 我们来看看你是否能口算出两个任意数相乘的结果
First of all we’ll see if you can multiplysome numbers together I’ll give you a question which is
题目是 21乘31
twenty-one times
thirty one.I’ll give you six seconds to work that out.
So time’s up.
如果你算出结果是651 那你做的很好 结果正确
So if you got the answer of 651you did really really well you got the right answer
如果你忙于找计算器 却没有及时找到 那就太糟了
If you were busily reaching for the calculator butcouldn’t find it in time bad luck
不过其实你根本就不需要计算器 我会展示如何快速算出结果
but you shouldn’t need a calculator, andI’ll show you how to work it out quickly
如果没做出来也别沮丧 我会教你的
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
结果是6 这就得出了结果的第一位数
is six, and we have the first part ofour answer
We leave a blank space.
要得到结果的最后一个数字 只要把两个数的末位相乘 即1×1=1
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
只要把这两个数相乘 这两个数相乘 然后结果相加
is multiply this number and this number and this number and this numberand we add the two answers together
也就是1×2=2 1×3=3
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
So, what about 43
times 21, a little bitharder this time
你会怎么算呢? 算好了吗?
See how you go.Have you got the answer yet?
I’ll start working through this one.
一样地4×2=8 留个空
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
这就有了一个问题 你也一定遇到了这个问题
Now this leads to a problem,so this is a little trick for to understand
这里只有一个空 只能填进一个数字
There is only one space hereWe only have space to fit one digit
So the digit it puts in out of this ten
那就应该是0 那么1的话
is the zero,and for the one
We carry this across And we add it on, so
结果就是1+8=9 结果是903
The answer we end up getting 1 + 8 is 9 0 3…nine hundred and three.
很好 再来一个
Very good.I think we can go through one more
把这里擦掉 再做一题
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
兴奋到跃跃欲试了 开始吧
Too excited, I can’t wait to get theanswer – let’s work it out
First number 4 x6Leave a space.
结果是24 空一格
is 24.Leave a space.
2×3=6 下一步
2 x 3 is 6 And then what we do
希望这次我没算错 我已经重做过视频了
And I hope not to get this wrong.I had to remake the video earlier
我偶尔也是会犯错的 我太兴奋了导致犯了错
as I stuffed up this one Occassionally I get all excited and I makemistakes too.
不过上传的油管视频我们是不会有错的 结果肯定是对的
But for YouTube videos we don’t make mistake.We always get 100% correct
OK OK We multiply
这两个数相乘 4×3=12
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?
应该把4填在这 2到这
We put the 4 there and2 there.
So what answer did we get?
Two thousan six hundred and forty six
这就是正确答案 很酷吧?
Hey that’s the right answer.Pretty cool right?
如果你稍作练习 一定会做的又好又快
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
your a genius alright?
别太自傲 大家可能因此而疏远你
I mean don’t go too far – peoplemight stop talking to you but hey –
但是 试一下 你真的会做的很好
you do this, you’ll doreally well.
你可能也会犯点错 我们都会犯错
And yes you may make a few mistakes.We all make them.
最后 给大家留点习题
So finally I will leave youwith a few questions
我会写下来 你可以暂停一下算出结果
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
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.
大家一定已经算出答案了 我们现在来算一下
OK so hopefully you’ve workedthrough those and we’ll go through the
answers right now.
OK so
2 x 3 is 6
空一格 2×2=4然后
We leave the blank space.2 x 2 is 4 and then we add four
and six together
which is ten. We get the answer704
The next one 5 x 6
空一格 1×3=3
is 30 Leave a space 1 x 3 is 3 and then we get
然后3×5=15 1×6=6
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
这里填1 这里是2
This will be a one, andthis will be a 2 so our answer is three thousand
结果是3213 最后一题
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.
So our answer is fourthousand
one hundred and eighty two
希望大家都做对了 下次见
I hope you did well on those.See you next time