Apply the Area Formula for Rectangles

Students use the formula A = l × w to find the area of rectangles in real-world and mathematical problems. Students also determine a missing side length when given the area and one dimension, applying division to find the unknown.

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Grade 4 · Area and Perimeter of Rectangles · question 1 of 3

0 of 20

20 rungs. A star at the top.

Find the area of shape A from its marked sides.

Your answer:

How it is taught

0:00 of 3:12

Area is the space inside a rectangle.

It equals length times width.

The answer is counted in square units.

Read it: Count inside, then around

A 4 by 5 frame of tiles sits on the page. Twenty cells fill the inside. The walk around the edge is a different number.

Count the cells inside: 4 rows of 5 make 20.
Walk the edge: 5 + 4 + 5 + 4.
Name both: 20 inside, 18 around.

Counting every cell one by one still works, but rows of 5 get you 20 with less losing track.

The walk around uses each side once; doubling 5 and 4 is the same walk.

Inside and around are two jobs on one frame: filling tiles is not the same as fencing them.

Count the cells inside, then add the four sides to walk around.

Adding 4 and 5 once and calling 9 the walk around, or using 20 for both jobs.

Walk all four sides: 5, 4, 5, 4. That is 18, not 20 and not 9.

A rectangle is 3 squares by 2. How many squares cover it? — 6. 3 rows of 2 squares: skip-count the rows — 2, 4, 6.

A = 8 × 5

Here's a rectangular garden. We want to find its area — the space inside.

Grade 4 · Finding the area of a rectangular garden

Here's our garden, shaped like a rectangle.

The length along the top is eight feet.

The width along the side is five feet.

For any rectangle, area equals length times width — that's our formula.

Let's plug in our numbers: eight times five.

Eight times five equals forty.

Because we're measuring space inside the rectangle, the units are square feet.

The area of the garden is forty square feet. Nice work!

Now you try. Find the space inside this rectangle. What is the area?

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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