Math 3: Perimeter

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3rd GradeMath
Elementary and Middle School3rd Grade
LanguageEnglish Language

Transcript

00:19

But they also need a more mathematical tool: the concept of perimeter. [Math problems floating around]

00:23

What's the concept of perimeter?

00:26

We're glad you asked!

00:27

…No seriously.

00:28

Otherwise, we would've made this entire video for nothing. [Kid with his hands on his hips looks unconvinced]

00:30

Perimeter is the distance around the outside of an object or a space.

00:34

So let's take a look at this pool.

00:36

And for now let's only look.

00:38

We only get to do cannonballs after the math is done. [Man goes to jump in the pool and stops midair]

00:41

If we want to measure the pool's perimeter, we need to measure the lengths of each of [An arm pulls the man away from the pool]

00:44

its four sides…

00:45

…and then add them all together.

00:47

So let's do it.

00:48

If we measure the width, we see that it's fifteen feet.

00:51

And if we measure the length, we see that it's twenty feet.

00:54

So to find the perimeter, we need to add one length…

00:57

…to one width…

00:58

…to the other length…

00:59

…and to the other width…

01:00

…which gives us the grand total of seventy feet.

01:02

Time for a celebratory cannonball! [Man jumps into the pool]

01:04

We should probably point out that longer perimeters don't necessarily mean that the object or

01:08

space will be bigger.

01:09

To see that, let's take a look at this pool. [Aerial picture of another swimming pool]

01:12

Like the first pool, this second one has a width of fifteen feet and a length of twenty

01:16

feet…

01:17

…but it also has a weird little square jutting into it, with each side measuring five feet.

01:21

So when we start adding up the lengths of the sides, we again need to add the two lengths

01:25

and one width…

01:26

…but this time we have to add all of those little five foot lengths that make up the

01:30

other side.

01:31

So this pool has a perimeter of 80 ft., which is longer than the first pool's perimeter, [Coop pointing at a blackboard]

01:36

even though it has less space inside.

01:38

That means that having a really long perimeter doesn't necessarily mean you'll have a better [Family in a pool]

01:42

pool party.

01:43

Who cares if you're in a pool with a perimeter of a hundred feet if you can barely move? [Man inside a paddling pool the shape of a duck]