Solve Real-World Perimeter Problems

Students will solve real-world problems involving perimeter, such as fencing a yard, framing a picture, or finding the border of a rug. They will distinguish between situations that require perimeter vs. area and justify their reasoning.

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Grade 3 · Perimeter of Polygons · question 1 of 3

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12 rungs. A star at the top.

Ava seals a triangular vent with sides 9 inches, 4 inches, and 6 inches. She also seals a square hatch with sides of 5 inches. Which opening needs more weatherstrip, and by how much?

How it is taught

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Perimeter is the distance around a real space.

Fences, frames, and curtains follow that outside path.

Read it: Walk the four sides

You have a 3 by 5 frame of squares. Counting every edge one by one is slow. The frame shows 15 inside and 16 around.

Walk the four sides of the frame: 5, 5, 3, 3.
Add them: 5 + 5 + 3 + 3 = 16 around.
Keep that apart from the inside count, which is 15.

Counting every tiny edge unit works, but it is slow and you lose track at the corners.

The 15 inside is how much space; the 16 around is how long the fence is.

Opposite sides match: two 5s and two 3s, so you add each pair once.

Add the four sides to walk around; the squares inside answer a different question.

Saying the walk around is 15 because there are 15 squares inside.

The 15 is the inside. Walk the four sides: 5 + 5 + 3 + 3 = 16.

A rectangle is 8 by 3. What is its perimeter? — 22. Walk around: 8 + 3 + 8 + 3 = 22.

Fence around an 8 ft by 5 ft garden

Here's Maya's garden. Her family wants to put a fence around it. How much fence do they need?

Grade 3 · How much fence does Maya's garden need?

Here's the garden — a rectangle. The top is eight feet long, and one side is five feet.

To buy enough fence, we need the perimeter — the distance all the way around the shape.

Let's walk around it. The top side is eight feet.

The right side is five feet.

The bottom is opposite the top, so it's also eight feet.

And the left side is opposite the right, so it's also five feet.

Now add all four sides: eight plus five plus eight plus five.

That adds up to twenty-six.

Maya's family needs twenty-six feet of fence to go all the way around. Nice work!

Now you try. Find how much fence this garden needs. How far around is it?

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics

Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal: 1 star — one skill mastered, every rung of its ladder climbed
Climbing now: Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

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