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## MAP Recommended Practice

### Unit 24: Lesson 7

Perimeter- Perimeter: introduction
- Perimeter of a shape
- Find perimeter by counting unit squares
- Find perimeter by counting units
- Finding perimeter when a side length is missing
- Find perimeter when given side lengths
- Finding missing side length when given perimeter
- Perimeter review

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# Perimeter of a shape

CCSS.Math:

Sal finds perimeter of various shapes. Created by Sal Khan.

## Video transcript

What is the perimeter
of the shape? Each square in the grid is
a 1 by 1 centimeter square. So all we have to do
is add up the lengths of these blue segments
right over here. And they put it
on this nice grid. And each box here is 1 by 1. So let's say we start up here. We want to make sure that we
only go to where we started and we don't double count. So this perimeter is 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
22, 23, 24 centimeters long. So it is 24 centimeters. The other way we could
have thought about this is you could have looked at the
length of each of these sides. So this is 1 plus 2
plus 3 plus 1 plus 3 plus 1 plus-- what is this--
5 plus 2 plus 4 plus 2. And you would have also
gotten 24 centimeters. Let's do a couple more of these. What is the perimeter
of the square? So once again, it's the
length of all of the segments that define the outside
boundary of the square. And by definition, a square--
all of its sides are equal. So you have 4 sides that
are all 7 meters long. So you could say it's
7 meters plus 7 meters plus 7 meters plus
7 meters, or it's 4 times 7 meters or 28 meters. Let's do one more. What is the perimeter
of the regular pentagon? So it's a regular pentagon,
which means all of its sides have the same length. And they give us a side of one. The length of one is 2. So all of the sides
have length 2. So it's going to be 2 plus
2 plus 2 plus 2 plus 2, or essentially five 2's. Or another way of
thinking about it is it's 5 times 2, which
is going to be 10. You have five sides
of this pentagon. Each of those sides
are 2 units long. So 2 units long times 5 sides
is going to be 10 units.