Multiplying 2 digit by 1 digit numbers within 100

- [Instructor] What I
wanna do in this video

is try to figure out what 3 times 29 is.

And there's a lot of
ways of approaching this,

but the way that we're
going to think about it

is using an area model.

What do I mean by that?

Well, we can imagine a
rectangle that is 3 units long

in the vertical direction,
or in that direction,

and then 29 units in this direction,

and this isn't drawn completely to scale.

And if you were to multiply
what 3 times 29 is,

you would get this area right over here.

So how can we use this area model?

Well, one way to do it

is to think about 29 as being
the same thing as 20 + 9.

So, for example,

let's say that this part right over here

is 20 units long, in the blue.

So I'm gonna split up this rectangle.

So that part right over
here is 20 units long,

and this part right over
here is 9 units long.

So this is 9,

and, to be clear, this
part right over here is 20.

And it's still 29 units long, or wide,

because 20 + 9 is 29.

Now the reason why this is useful

is I can now think about
these different areas.

I can now think about
this area right over here.

It's 3 units high and 20 units wide.

So what's this area?

Well, this area is going to be 3 times 20,

which we can do in our
head, 3 times 2 is 6,

so 3 times 20 is 60 of these square units.

And then we could also
think about this area

right over here.

This area is going to be 3 times 9,

which you might already know is 27.

So if you wanna figure
out the entire area here,

which would be 3 times 29,

you would just add the 60 plus the 27,

so I could write it here maybe,

this is 60 + 27,

which is going to be equal to,

60 + 20 is 80 plus another 7,

is going to be 87.