MATHEMATICSPerimeter

Lesson Objectives

•The aim of this powerpoint is to help you…

• to find missing side lengths

• to find perimeters of shapes

What is ‘Perimeter’?

• Perimeter is the distance all the way around the outside of a shape.

• You ADD all the individual distances of every side (around the outside) together.

• However, you may need to work out missing sides first!

What is the perimeter measured in?

• Perimeter is a distance (or length).

• Its metric units are millimetres (mm), centimetres (cm), metres (m) or kilometres (km).

• Its imperials units are inches (in), feet (ft), yards (yd) or miles.

Missing Sides

• To find missing sides…

• Look for symbols to show whether sides have the same length (a small line going through two or more sides/lines)

• Compare the missing side with the lengths of other parallel sides and work out the difference or sum (as appropriate).

Example 1

• This is a triangle

• Although I have only been given one side, the little lines through each side show they are all of equal length

• All three sides are 8m

• P = 8m + 8m + 8m = 24m

8m

Example 2

• Here is an L-shape

• Before we calculate its perimeter, we need to work out the length of the red side.

2mm

5mm

8mm 4mm

6mm

Example 2 (cont’d)

• Here are the isolated vertical sides of the L-shape

• The red side is vertical and is found by taking the green side away from the yellow side

• Now we have all side lengths

5mm

8mm

(8mm – 5mm =) 3mm

Example 2 (cont’d)

• Start at the top left and move in a clockwise direction:

Perimeter =

2mm + 5mm + 4mm + 3mm + 6mm + 8mm = 28mm

2mm

5mm

8mm 4mm

3mm

6mm

Quick Practice

• Find the perimeter of each of these shapes. 3mm 7mm

6mm 11mm

2m

2m

7cm 3m 9m

2m

12cm 8m

7mm

Quick Practice - Solutions

7cm

12cm

7cm

12cm

This side is the same as the 12cm on the bottom

This side is the same as the 7cm on the right

7cm

12cm

So the perimeter is: 12 + 7 + 12 + 7 = 38cm

Quick Practice - Solutions

3mm 7mm

6mm 11mmThis side is the same as the 11mm on the right hand side

This side goes all the way across from left to right so is the same as the 3mm + 6mm + 7mm = 16mm

7mm

This side is the same as the 7mm on the right hand side of the dip

7mm11mm

16mm

So the perimeter is: 3 + 7 + 6 + 7 + 7 + 11 + 16 + 11 = 68mm

Quick Practice - Solutions

2m 2m

9m 2m

8m

3m

2m 2m

9m 2m

8m

3m

Top to bottom (using right hand side) = 2 + 9 = 11Top to bottom on left hand side must also equal 11, so this side must be 9 (+ 2 = 11)

9m9m

So the perimeter is: 2 + 2 + 9 + 9 + 8 + 2 + 3 + 9 = 44m

Left to right (using bottom sides) = 3 + 8 = 11Left to right using top sides must also equal 11, so this side must be 9 (+ 2 = 11)

What next?• Print out the notes called PAV1-Perimeter. Read through

them and make sure you answer any questions.

• Work through the MyMaths lesson and then its online homework called Perimeter found at:

• http://app.mymaths.co.uk/265-resource/perimeter• http://app.mymaths.co.uk/265-homework/perimeter

• Save and complete the worksheet: Perimeter-S1.xlsx

• Now move on to the PAV2a powerpoint