Adding three digit numbers with regrouping | Addition and subtraction | Arithmetic | Khan Academy

We have three different addition
problems right over here.

And what I want you to do so
you get the hang of things

is to pause the video
and try them on your own.

But as you do them, I want
you to really keep in mind

and think about what the
carrying actually means.

So I assume you've
tried it on your own.

Now I'll work through
them with you.

So we have 9 plus 6.

9 ones plus 6 ones.

Well 9 plus 6 is 15.

Well, we can write the
5 in the ones place,

and then we can carry the one.

But what did we just do?

W.hat does this 1 represent?

Well, we put it in the tens
place-- one 10 represents 10.

So all we've said is that 9
plus 6 is equal to 10 plus 5.

Is equal to one 10 plus
5, which is equal to 15.

Now, in the tens place, we have
1 plus 0 plus 9 which is 10..

So we can write 0 and carry
the 1 1 plus 0 plus 9 is 10.

Now what does that really mean?

Well this is 1 ten plus 0 tens
plus 9 tens, which is 10 tens.

10 tens is 100.

Or another way to think
about 100, it's 1 hundred,

and 0 tens.

So that's all that
carrying represents.

So now we have a 1,
plus a 7, plus a 9.

That is going to be 17.

Now we have to remind ourselves,
this is in the hundreds place.

This is actually 1 hundred
plus 7 hundred plus 9 hundred

17 hundred.

Or 1 thousand, 7 hundred.

And of course we
have this 5 here.

And we are done.

Now let's try to
tackle this one.

Now the reason why
I wrote it that way

is to make sure that we
remind ourselves to align

the proper places under
the appropriate places.

So this we rewrite as-- let me
do that same green color-- we

could rewrite this
as 373 plus-- we

want to write the ones
place under the ones place,

and the tens place
under the tens place,

so that we're adding
the appropriate values.

So 3 plus 8 is 11.

The 1 in the ones place,
and the 1 in the tens place.

10 plus 1 is 11.

1 plus 7 is 8.

8 plus 8 is 16.

This is actually 16 tens.

So let me just
write down the 16.

What is 16 tens?

Well, that's 160.

So this 6 is a 60, and
then I have a hundred.

1 plus 3 is 4.

But these are actually
hundreds, so it's 4 hundreds.

So we get 461.

Now finally, 9 plus 3 is 12.

2 ones, and 1 ten.

12 is the same
thing as 10 plus 2.

Now in the tens place,
1 plus 4 plus 9 is 14.

So we write the 4,
and carry the 1.

But remind ourselves this
is actually 10 plus 40

plus 90, which is 140.

Which is the same
thing as 40 plus 100.

And then 1 plus 1 plus 2 is 4.

But this is the hundreds place.

So this is actually 1 hundred,
plus 1 hundred, plus 2 hundred,

or 4 hundred.

And we're done.