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## 3rd grade

### Course: 3rd grade > Unit 10

Lesson 2: Count unit squares to find area- Intro to area and unit squares
- Measuring rectangles with different unit squares
- Find area by counting unit squares
- Compare area with unit squares
- Creating rectangles with a given area 1
- Creating rectangles with a given area 2
- Create rectangles with a given area

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# Intro to area and unit squares

Sal covers figures with square units to find their area. Created by Sal Khan.

## Want to join the conversation?

- how does area help the real world(32 votes)
- I find geometry has many practical uses in everyday life, such as measuring circumference, area and volume, when you need to build or create something. Geometric shapes also play an important role in common recreational activities, such as video games, sports, quilting and food design, ect...(6 votes)

- how he finds the amount is by using unit square(8 votes)
- Using units squared will give you the answer as long as the shape you are measuring can be divided by the area of units squared. So doing this in a mathematical sense without using physical shapes, you would divide the Unit squared by the objects area. Ex. How many times would a 1cm unit go into a 3cm unit, 3 times. Because we multiplied the 1cm unit x3 to get our answer.(1 vote)

- What is it called when it is 4-D(example:3-D,cube units/2-D,square units)?(5 votes)
- There's no name for it yet...

Scientists suggest that 4 Dimensional could be time.(3 votes)

- What if the square unit is cut in half? Would it be some number .5(4 votes)
- Yes, you would have to think of it as 1/2 unit square.(5 votes)

- So are we going to write it down(5 votes)
- If segments intersect at points or vertices then

determining the length of sides/segments which side includes the point of intersection and which side excludes it, both the sides cannot have it right??(2 votes)- Points have no dimension.

You may want to review the intro video for Geometry that covers a lot of the basics: https://www.khanacademy.org/math/basic-geo/basic-geo-lines/lines-rays/v/language-and-notation-of-basic-geometry(7 votes)

- how do find the area of a triangle?(2 votes)
- The formula:
`A = (b * h) / 2`

The area is the base times the height, divided by 2.

So, if we had a triangle with a base of 2 and a height of 10, we would do.`A = (2 * 10) / 2 = 20 / 2 = 10`

Area is 10.(6 votes)

- how do you find the prminiter(2 votes)
- To find the perimeter, find the total number of units (distance) around the edges of the shape.

Have a blessed, wonderful day!(4 votes)

- How can I use the cubes.(4 votes)
- What if you have a square but you also have round unit?(2 votes)
- I'm sure circles are in a more advanced part of geometry.(5 votes)

## Video transcript

So we've got two
figures right over here, and I want to think about
how much space they take up on your screen. And this idea of how much
space something takes up on a surface, this idea is area. So right when you look at
it, it looks pretty clear that this purple figure
takes up more space on my screen than
this blue figure. But how do we
actually measure it? How do we actually know how much
more area this purple figure takes up than this blue one? Well, one way to do
it would be to define a unit amount of area. So, for example, I could create
a square right over here, and this square, whatever units
we're using, we could say it's a one unit. So if its width right
over here is one unit and its height right
over here is one unit, we could call this
a unit square. And so one way to measure
the area of these figures is to figure out how many
unit squares I could cover this thing with
without overlapping and while staying
in the boundaries. So let's try to do that. Let's try to cover each of
these with unit squares, and essentially we'll
have a measure of area. So I'll start with
this blue one. So we could put 1, 2, 3,
3, 4, 5, five unit squares. Let me write this down. So we got 1, 2, 3,
4, 5 unit squares, and I could draw the
boundary between those unit squares a little bit clearer. So we have 5 unit squares. And so we could say that
this figure right over here has an area. The area is 5. We could say 5 unit squares. The more typical
way of saying it is that you have 5 square units. That's the area over here. Now, let's do the same thing
with this purple figure. So with the purple figure, I
could put 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 of these unit squares. I can cover it. They're not overlapping,
or I'm trying pretty close to not make them overlap. You see, you can fit 10 of them. And let me draw the
boundary between them, so you can see a
little bit clearer. So that's the boundary
between my unit squares. So I think-- there you go. And we can count them. We have 1, 2, 3, 4,
5, 6, 7, 8, 9, 10. So we could say the area
here-- and let me actually divide these with the
black boundary, too. It makes it a little bit
clearer than that blue. So the area here for the
purple figure, we could say, so the area here is equal to 10. 10 square, 10 square units. So what we have
here, we have an idea of how much space does
something take up on a surface. And you could eyeball
it, and say, hey, this takes up more space. But now we've come up with
a way of measuring it. We can define a unit square. Here it's a 1 unit by 1 unit. In the future we'll see that
it could be a unit centimeter. It could be a 1 centimeter
by 1 centimeter squared. It could be a 1 meter
by 1 meter squared. It could be a 1 foot
by 1 foot square, but then we can use
that to actually measure the area of things. This thing has an area
of 5 square units. This thing has an area
of 10 square units. So this one we can actually
say has twice the area. The purple figure
had twice the area-- it's 10 square units--
as the blue figure. It takes up twice the amount
of space on the screen.