In this activity, we're going to practise how to calculate the perimeter of some shapes.

Perimeter is the distance around the outside of a shape.

Usually, we are given at least some of the measurements when we are asked to calculate the perimeter of a shape.

We need to use these measurements to work out those that we're not given.

Sounds a little tricky, but it's nice and easy. Let's have a look!

Here is a rectangle.

We are given the length of two sides.

We know that opposite sides are equal in a rectangle.

Therefore, we know that two sides are 15 cm and two sides are 10 cm.

To **calculate the perimeter** we need to **add the lengths of all four sides** together.

10 + 10 + 15 + 15 = 50 cm

The perimeter of the rectangle is **50 cm**

Let's have a look at another example.

Here is a rectilinear shape.

We can see that this shape has six sides.

The length of each side is given to us.

We need to add all of the measurements to find the perimeter (there will be six to add)

1 m + 5 m + 4 m + 2 m + 3 m + 3 m = 18 m

The perimeter of the shape is **18 m.**

We must remember to put the unit of measure.

Now, why don't you have a go at some questions like these?