How to Figure Out Perimeter for Numeracy Test Questions

By Colin Beveridge

The perimeter of any shape is the distance all the way around it. You can work it out by just adding up the lengths of the sides.

For example, if you know a square has sides of length 10cm, you can work out that the perimeter is 10cm + 10cm + 10cm + 10cm = 40cm.


The other shape is a bit harder to figure out, but with a bit of thinking it all comes together. Here are the steps for working out the perimeter of a complicated shape:

  1. Find out which sides don’t have a length marked.

    In this case, the vertical side in the top-right and the horizontal side at the top have no length marked.

  2. Work out the length of those sides using other facts you know about the shape to help you.

    The vertical side in the top-right has to be 5m because the two vertical sides on the right have to match up with the one vertical side on the left. The left side is 11m, and the lower-right side is 6m, so there’s 11 – 6 = 5m left to fill. Using the same kind of thinking, the horizontal side at the top has to be 7m long.

  3. Write down all of the sides’ lengths.

    Here, the sides are 10, 6, 3, 5, 7 and 11m long.

  4. Add the lengths up. The answer is the perimeter.

    The sum is 10 + 6 + 3 + 5 + 7 + 11 = 42, which is the answer.