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Number Trail Grade 3 / Week 11 / Thursday
4/6
Week 11 · Area and perimeter

Thursday

The garden fence
// Cover it with squares, walk around the edge
⏱ about 15 min

Thursday: The garden fence

Chris the Coyote tips his feather hat and begins.

"Hazel once planted a rectangle garden, 8 meters long and 5 meters wide."

"She wanted a fence all the way around it."

"So she walked the edge and added each side: 8, 5, 8 and 5."

"That made 26 meters of fence."

"The distance around a shape is called the perimeter."

Learn it: perimeter

Perimeter is the distance all the way around a shape.

Add the lengths of all the sides.

A rectangle 8 m long and 5 m wide

Hazel's garden: 8 + 5 + 8 + 5 = 26 meters.

Area tells how much space is inside. This garden has area 8 × 5 = 40 square meters.

FIND THE PERIMETER
  • Read the question.
  • Tap your answer.
A rectangle 8 m long and 5 m wideWhat is the perimeter in meters?
A rectangle 6 cm long and 4 cm wideWhat is the perimeter in centimeters?
A rectangle 9 ft long and 2 ft wideWhat is the perimeter in feet?
A rectangle 7 in long and 7 in wideWhat is the perimeter in inches?
SHAPES WITH MORE SIDES
  • Read the question.
  • Tap your answer.
A triangle garden has sides of 5, 6 and 7 meters. What is its perimeter?
A pentagon has 5 sides, each 4 inches long. What is its perimeter?
A hexagon has 6 sides, each 3 cm long. What is its perimeter?

Find the missing side

If you know the perimeter, subtract the sides you know.

WHAT IS THE MISSING SIDE?
  • Read the question.
  • Tap your answer.
6 + 4 + 6 + ? = 20
2 × 9 + 2 × ? = 30
5 + 7 + ? = 18

Same perimeter, different area

Three rectangles: 1 by 5, 2 by 4 and 3 by 3. Each has perimeter 12.

But their areas are 5, 8, 9 square units. Same perimeter, different areas!

COMPARE THE RECTANGLES
  • Read the question.
  • Tap your answer.
Which rectangle has perimeter 12 and the biggest area?
Which rectangle has area 12 and the biggest perimeter?
SentenceTrue or false?
8 + 5 + 8 + 5 = 26?
Perimeter is the space inside a shape.?
5 + 6 + 7 = 18?
A 2 by 4 rectangle and a 3 by 3 rectangle have the same area.?
WHY THIS EXERCISE2 × 4 = 8 and 3 × 3 = 9. Same perimeter, different areas.
Try it
Take a piece of string and lay it around a book.
Mark where the string meets itself.
Measure the string with a ruler. That is the perimeter.
Draw two rectangles with the same perimeter but different areas.

What a fence! Tomorrow Freddy has an area and perimeter game.

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