7. PERIMETER
Lets look at a few and see if it’s the
width or the length.
If its width put your finger on your
nose.
If its length put your hand on your
head.
9. Example 1: the diagram
represents a pen for Jim’s pigs.
How much fencing does he need
to go around the plot?
4
m
4m
5m
5m
10. Here the length is 5m and the
width is 4m.
The perimeter of the plot is
5+4+5+4 =18.
So he needs 18m of fencing.
4
m
4m
5m
5m
11. Example 2: The diagram
represents a pond that needs a
low railing round the boundary.
Sally is working out the perimeter.
80cm
1.2m
Caution: all measurements used in
the calculation must be the same
units.
12. So we know that 100cm = 1m
There are 2 zeros so we move
the decimal point 2 places to the
left.
80cm becomes 0.8m
80cm
1.2m
Caution: all measurements used in
the calculation must be the same
0.8m
13. Now that our numbers all have the same
units we can add.
1.2m
0.8m
1.2 + 0.8 +1.2 + 0.8 = 4.0
So the perimeter is 4m. Don’t forget
to label your answers!
14. RECTANGLES AND SQUARES
In a rectangle the opposite sides are equal,
so to work out the perimeter of a rectangle
you just need to know the length and width.
15cm
6cm
What is the length and what is the width?
15. PERIMETER
There are three different methods to finding
the perimeter.
Method 1: add all the numbers together.
15cm
6cm 6cm
15cm
15 + 6 + 15 + 6 = 42cm
16. PERIMETER
Method 2: Because opposite sides are equal
you can also work out the perimeter in this
way: double the length, double the width,
then add the results together.
15cm
6cm 6cm
15cm
(15 X 2) + 6 X 2) = 30 + 12 = 42cm
17. PERIMETER
Method 3: The last method just adds the
length and width then doubles it.
15cm
6cm 6cm
15cm
15 + 6 = 21 21 X 2 = 42cm
18. PERIMETER
The method you choose is up to you- each
one will give the same answer.
Lets see what you have learned. Find the
answer to each question.
Once you have found the answer put you
hands on you head like this so I know your
finished.
