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3.1 Measuring the perimeter of irregular shapes

Example: How to measure the perimeter of an irregular shape

How would you measure the perimeter of an irregular shape – an L-shaped room, for instance – if you didn’t have all of the measurements that you would need? Watch the following video to find out.

Transcript (opens in new window)

Now try the following activity. Remember to check your answers once you have completed the questions.

Activity 8: Finding the perimeter

Note that you can assume that all of the corners in the images in this activity are right angles.

  1. A gardener decides to lay a new path next to his lily pond. The drawing shows the dimensions of the path.
    Figure 18 A pathway

    The gardener decides to paint a white line around the perimeter of the path. What is the perimeter of the path?

  2. A tourist information centre has a new extension.
    Figure 19 A new extension

    The tourist board wants to attach a gold strip around the border of the floor of the building. What is the perimeter of the new extension?

Answer

  1. To calculate the missing sides you should have carried out the following calculations:

    • 14 – 3 = 11
    • 15 – 1.5 = 13.5

    Now that you have found the missing sides, you can add them all together:

    • 15 + 14 + 1.5 + 3 + 13.5 + 11= 58 m

  2. To calculate the missing sides you need to carry out the following calculations to calculate the perimeter:

    • 5 – 2 = 3
    • 6 – 2 = 4

    Now that you have found the missing sides, you can add them all up together to calculate the perimeter:

    • 6 + 3 + 3 + 1 + 1 + 2 + 2 + 4 = 22 m

Summary

In this section you have learned how to work out the perimeter of both simple and irregular shapes.

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OpenLearn - Everyday maths 1 (Northern Ireland)
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