A2 初級 73 タグ追加 保存
In this video, I'll introduce you
to a new way of computing division,
especially for larger numbers.
And then we'll think a little bit about why it works.
So we're going to try to compute what 96 divided by 4 is.
And I'm going to write it a little bit differently.
I'm going to write 96 divided by-- so I'm
going to write this strange-looking symbol
right over here, this thing that covers the 96.
But you could view this as 96 divided by 4.
And I'll show you in a second why we write it this way.
This is actually a very useful way of actually computing it.
So the first thing we'll do is we'll say, well,
how many times does 4 go into 9?
Well, we know that 4 times 2 is equal to 8 and that 4 times 3
is equal to 12.
So 3 would be too much.
We would go above 9.
So we want to be below 9 but not have too much left over.
We want the largest number that gets us
into 9 without going over 9.
So we'll say it goes two times.
4 goes into 9 two times.
And then we say, what's 2 times 4?
Well, 2 times 4 is 8.
4 times 2 is 8.
Or 2 times 4 is 8.
And now, we subtract.
We subtract the 8 from the 9.
And we get 1.
And now we bring down the next digit, which is the 6.
And then we ask ourselves, well, how many times
does 4 go into 16?
Well, in this case, we know that 4 goes into 16 exactly
four times.
4 times 4 is 16.
So we say 4 goes into 16 four times.
Then we multiply 4 times 4 is 16.
We subtract.
And 16 minus 16, we have absolutely nothing left over.
And there we have our answer.
I know it seems kind of magical at this point.
But in a few seconds, we're going
to think about why this actually worked.
We got that 96 divided by 4 is equal to-- I
want to do that in a different color-- 24.
Now, what I want you to do right now is pause this video
and think about why did this actually work.
How did we magically get the right answer here?
And you can verify this.
Multiply 4 times 24, and you will get 96.
Well, I'm assuming you gave a go at it.
And the important thing always is
to keep track of the place value.
And it really tells you what's going
on when we do this process.
When we looked at this 9 right over here,
this 9 is in the tens place.
This is actually representing 90.
It represents 9 tens.
So we're saying, well, how many times
does 4 go into 90 if we're thinking about multiples of 10?
Well, it goes 20 times.
4 times 20 is 80.
And so we said, well, 4 times 20 is 80.
But we still have 16 left over.
You do 96 minus 80.
You have 16 left over to divide 4 into.
And then 4 goes into 16 four times.
So really, a lot of this is just saying, well,
we first figured out that we could go 20 times.
And then we said, well, that doesn't get us
all the way to 96.
We have to go another four times.
Hopefully, that helps.


Dividing numbers: intro to long division | 4th grade | Khan Academy

73 タグ追加 保存
Yrchinese 2017 年 2 月 5 日 に公開
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