IXL | Relationship between area and perimeter: find the area

The rectangles below have the same perimeter.

5 km

9 km

What is the area of the purple rectangle?

square kilometers

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Learn with an example

question

The rectangles below have the same perimeter.

3 ft

7 ft

1 ft

What is the area of the orange rectangle?

square feet

key idea

Rectangles with the same perimeter can have different areas.

solution

Find the perimeter of the green rectangle.

3 + 7 + 3 + 7 = 20

Both rectangles have a perimeter of 20 feet. Find the missing side length of the orange rectangle.

You know that two sides of the orange rectangle are 1 foot long. Subtract from the perimeter to find the combined length of the other two sides.

20 − 1 − 1 = 18

So, the combined length of the two other sides is 18. Divide by 2 to find the length of each of those sides.

18 ÷ 2 = 9

The orange rectangle is 9 feet by 1 foot. Find its area.

9 × 1 = 9

The area of the orange rectangle is 9 square feet.

Looking for more? Try these:

Lesson: Rectangles

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Teacher tools

Work it out

Not feeling ready yet? These can help:

HH.3Find the perimeter of rectangles using formulas

HH.2Perimeter: find the missing side length

OO.10Find the area of rectangles and squares

Lesson: Rectangles

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