Practise Calculating the Perimeter of Composite Shapes

In this activity, we're going to be calculating the perimeter of some composite rectangles.

We know that the perimeter of a shape is the total distance around the outside.

 

 

If each side of this square is 15 cm, we know that the perimeter will be 60 cm (4 x 15 = 60)

 

A composite/compound rectangle is any shape that is made up of two or more rectangles (including squares).

The shape below is made up of two rectangles.  It is a composite rectangle.

In this composite rectangle, all of the measurements are provided so we can easily work out the perimeter: 18 m

Add all the lengths together: 5 m + 4 m + 2 m + 3 m + 3 m + 1 m = 18 m

 

 

Here is a composite rectangle where some of the measurements are missing.

We need to find the missing measure using the information we are given in order to calculate the perimeter.

 

 

There are six sides to the shape, so we will have six measures to add.

We know that opposite sides of a rectangle are equal, so we can see that the 4 cm + ? must equal 10 cm.

10 cm - 4 cm = 6 cm

The missing measure is 6 cm.

Now, we can add all of the measures to find the perimeter:  3 + 6 + 5 + 4 + 8 + 10 = 36 

The unit of measure is cm - we must include this in our answer.

The perimeter of the shape is 36 cm.

 

Top Tips:

Use the information given to work out missing measures.

Check the unit of measure and remember to include it in your answer.

Check the number of sides each shape has and make sure you have included them all.

 

Good luck!