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Lesson · Grade 6 · Mathematics

Perimeter of a Complex Shape: Find the Missing Sides First

  • Grade 6
  • Mathematics
  • 1 min 9 s
  • British Columbia
  • BC6-MA-29

An L-shape has six sides but only four labelled, so the video first works out the two missing ones by sliding copies of sides into place: 10 − 3 = 7 cm and 8 − 2 = 6 cm. It then adds all six sides on one trip around the shape to get a perimeter of 36 cm.

Concept: Perimeter of a complex shape

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In one sentence

The question this lesson answers

What is the perimeter of this shape?

Perimeter is the distance all the way around a shape.

Transcript

What the lesson says

What is the perimeter of this shape?

Perimeter is the distance all the way around a shape.

This shape has 6 sides, but only 4 of them are labelled.

So first, we find the 2 missing sides.

Together, the 2 top sides are as long as the bottom side.

So this missing side is 10 minus 3, which is 7 centimetres.

Together, the 2 right-hand sides are as long as the left side.

So this missing side is 8 minus 2, which is 6 centimetres.

Now we know all 6 sides, so we add them all, going around the shape.

3 plus 6 plus 7 plus 2 plus 10 plus 8 is 36.

So the perimeter of this shape is 36 centimetres.

To find the perimeter, work out any missing sides first, then add up every side.

Curriculum

Where this fits

British Columbia, Grade 6

Mathematics, Geometry and measurement: perimeter of complex shapesBC6-MA-29

Next: Area of a Parallelogram: Cut and Slide into a Rectangle

The outcomes and strands follow the British Columbia curriculum.

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