Multiplication 3: 10,11,12 times tables

Multiplication 3: Learning to multiply 10, 11, and 12.

In the last video we went over the multiplication tables for one through nine

and I ran out of time, and actually, it was a good thing

because one through nine are kind of the core multiplication tables.

And you'll see that if you know all your multiplication tables from one to nine,

so you know any number between one and nine

times any other number between one and nine,

you can actually do any multiplication problem out there.

But what I want to do now

is I want to complete the multiplication tables for ten, eleven, and twelve.

So what is ten times-- let's just start with zero.

Ten times zero.

Anything times zero is zero.

Ten zeros are zero.

Zero plus zero plus zero ten times is still zero.

What's ten times one?

Ten times one.

Well that's just ten one time.

Or one plus itself ten times.

That's ten.

I think this is second nature to you at this point.

What's ten times two?

Ten times two.

I meant to switch colors, but I didn't.

Ten times two?

That's ten plus ten, which is twenty.

Fair enough.

And notice, we went up by ten the first time.

We went up by ten again to get to twenty.

What's ten times three?

Well, that's ten plus ten plus ten,

or we could view it as ten times two plus another ten,

which is equal to thirty.

What's ten times four?

I think you start to see a pattern.

Ten times four is equal to forty.

Notice, ten times four is equal to forty.

If I were to ask you what is ten times--

let me do another color-- five?

Well that's equal to fifty.

Ten times anything is that anything with a zero behind it.

So the ten times tables,

you almost don't have to remember it.

So let's just keep going.

What's ten times six?

It's equal to sixty.

Six zero.

What's ten times seven?

Seventy.

Ten times eight?

This is almost ridiculous.

Ten times eight is eighty.

Ten times nine?

Ninety.

Ten times ten?

Now this is interesting.

Ten times ten, so it'll be a ten--

let's see me write this.

Let me do it in this orange color.

Ten times ten.

So it'll be ten tens or a ten with a zero behind it.

There you go. Notice, whatever number times ten, I just add a zero,

then I get the next number.

So it's one hundred.

And I think you understand why that is.

I added ten to itself ten times.

That each ten-- you go from ten, twenty, thirty.

Thirty is just three tens or ten times three.

Ninety is just nine tens or nine times ten.

Let's keep going.

So ten times eleven is equal to eleven with a zero behind it.

One hundred and ten.

Finally, ten times twelve is equal to one hundred and twenty.

Now, just for fun, these are kind of your ten times tables.

But now that you know the pattern you can do anything.

If I asked you what five thousand seven hundred thirty-two times ten is,

what's it going to be?

It's going to be this number with just one more zero.

So it's going to be-- I won't read it out yet.

Five seven three two with a zero behind it.

And just so you know,

this little comma that I wrote in the number there,

that's just to make it easier for me to read that number.

So, you put the comma-- you start over here

and every third number you put the comma.

So here I'm going to put the comma right here.

I'm going to put the comma right there.

So now I can read this.

The comma doesn't really add or take anything away from the number,

it just helps me read it.

Now five thousand seven hundred thirty-two times ten is fifty-seven thousand three hundred twenty.

I just had to add a zero there,

but that was a pretty straightforward multiplication.

And notice, we had five thousand times ten

and we got to fifty-something thousand when we multiplied them.

So that's similar to five times ten is equal to fifty.

But instead of five I had a five thousand,

and so I got a fifty thousand and something and all this other stuff.

We're going to learn more about how to do problems like this in the future.

But I thought I would introduce you to the idea

that just from this little pattern of adding a zero,

you already know your tens times tables.

Now let's do our elevens.

Our elevens, Elevens get a little bit--

Well, they start off easy,

and then they get a little more difficult as we get into high numbers.

So, eleven times zero.

This is easy, this is zero!

Eleven times one.

This is also easy!

It's eleven!

Eleven times two.

We're going to start seeing a pattern here.

It's eleven plus eleven or we could've added two to itself eleven times,

but that is equal to twenty-two.

If we do eleven times three, it is equal to thirty-three.

Eleven times four is equal to forty-four.

I think this is becoming obvious to you.

What's eleven times five?

Eleven times five is fifty-five!

Notice I put the five twice.

What's eleven times six?

It's sixty-six!

Eleven times seven is eighty-four-- no!

I'm kidding!

I didn't want to mess with you like that.

But no.

Of course, it's seventy-seven!

Seventy-seven.

You just repeat the number twice.

Seventy-seven.

Let me switch colors.

Eleven times eight is equal to eighty-eight.

Eleven times nine is equal to ninety-nine!

Now what's eleven times twelve?

Eleven times twelve.

Oh sorry, I skipped ten.

Eleven times ten.

You might want to say it's "tenty-ten!"

No!

That's wrong!

It's not "tenty-ten!"

So that little pattern that we had

where you just repeat the number,

that only works for one digit numbers.

So it only works for one through nine.

Eleven times ten--

well, we could think about it a couple of ways.

We can add eleven to ninety-nine.

So we can say it's ninety-nine plus eleven.

And what's that?

That's equal to one hundred and ten.

And I'm going to show you how to do--

well, hopefully you've already watched the video on how to add two-digit numbers like this,

but that's one hundred and ten.

Or you could just use the property from the tens times tables that we learned.

Where if you just take eleven times ten, you add a zero to the eleven,

you get one hundred ten.

That's the eleven right there.

Finally, let's do eleven times twelve.

Eleven times twelve.

No easy way to remember this,

you just kind of should remember it.

Or you could say look,

it's going to be eleven more than eleven times-- sorry.

I keep skipping things.

We should do eleven times eleven first.

Let me make sure this is clear.

We're doing eleven times eleven before we go to eleven times twelve.

So eleven times eleven is going to be eleven more than eleven times ten.

So we add eleven to this.

Eleven plus one hundred ten is one hundred twenty-one.

And actually, as you'll see,

there actually is an order as we get to higher multiples of eleven,

but I'll leave that to a future video.

And then finally, we're at eleven times twelve.

Eleven times twelve.

And we could add eleven to itself twelve times.

We could add twelve to itself eleven times.

Or we could just say,

hey, it's going to be eleven more than eleven times eleven.

So that is what?

You add eleven to this.

What do you get?

You get one hundred thirty-two.

I just added one hundred twenty-one plus eleven

and then got one hundred thirty-two.

Now the other way you could have said it is, well,

what's ten times twelve?

Ten times twelve,

we already knew that.

That was one hundred twenty.

So eleven times twelve,

because we're multiplying twelve by one more

should be twelve more than that.

So that should be one hundred thirty-two.

So two ways to get the exact same answer.

All right! Now let's do our twelve times tables.

Twelve times tables.

And once you know this

you are ready to tackle any type of multiplication problem.

But we'll do that in future videos.

So twelve times zero.

Super easy! Zero.

Twelve times one.

Also super easy!

Is twelve.

Now it gets interesting.

We're going to increase by twelve every time.

Twelve times two is equal to twenty-four.

Twelve plus twelve is twenty-four, right?

Twelve times-- not twenty-two.

Let me rewrite that.

Twelve times three is going to be twelve plus twelve plus twelve.

Or we could write that as twelve times two.

I see my brain is doing the wrong things.

We could rewrite that as twelve times two plus twelve.

Or we could rewrite that as twenty-four plus twelve.

Either way, all of these get us to thirty-six.

And notice, that's just that plus twelve.

Twelve times four.

Twelve times four is equal to forty-eight.

There's a lot of ways you could think about it.

You could say eleven times four is forty-four.

Right? Eleven times four is equal to forty-four.

And you go up by one more four, so you get to twelve times four.

Or you could say twelve times three is thirty-six

and you can add one twelve to it to get to forty-eight.

Either way works,

and that's because you can multiply in either direction.

Let's keep going.

Twelve times five is equal to sixty.

Ten times five is fifty, eleven times five is fifty-five,

so twelve times five is sixty!

Twelve times six is equal to what?

It's going to be twelve more than this.

It's going to be equal to seventy-two.

Twelve times seven.

Twelve more than this again.

Twelve more than seventy-two is eighty-four.

And I'm serious, you know, I'm probably a lot older than you are,

and I still, in my head to confirm,

I go to some twelve times tables that I remember as definitely right.

Like oh, twelve times five-- and sometimes in my head I say,

oh, let me add another twelve.

Oh yeah, definitely, my memory was correct.

Twelve times six is seventy-two.

All right.

Then you go to twelve times eight.

Add twelve to the twelve times seven.

Ninety-six.

Twelve times nine.

Well you add twelve to this, so it's one hundred eight.

One hundred eight.

And then twelve times ten.

This is an easy one!

Right? We just add a zero to the twelve to get one hundred twenty.

Or we could've added twelve to one hundred eight.

Either way.

Twelve times eleven.

We just did this.

You add twelve to this to get one hundred thirty-two.

And then twelve times twelve,

is equal to one hundred forty-four.

And this actually shows us--

If I had a dozen of a dozen eggs-- a dozen is twelve.

Or if I had a-- I think a gross is actually twelve dozens.

So that's one hundred forty-four eggs.

So you'll actually end up seeing this number a lot.

More than you would expect in life.

But anyway, we've now completed all of our multiplication tables.

And I really encourage you to take the time now to go and memorize them.

Make some flash cards.

Use the little software thing that I wrote on my website.

You could try that out.

As of September Two Thousand Nine, it's working.

I haven't touched it in a while, but I'm actually probably going to rebuild it soon.

So if you're watching this video in the year Two Thousand Two Hundred--

Well, I would probably not exist anymore.

But hopefully you'll get a better version of the software app.

But you should practice it.

You should get your parents to quiz you.

You should get notes cards.

You should just be mumbling to yourself as you walk to school--

What is twelve times nine?

What is eleven times eleven?

And you should quiz each other,

because it'll pay huge rewards to you later on in life.

See you in the next video!