Composite Figures

1
Composite Figures

• Pieces of the Whole

2
Bill is painting his basement floor.
2.3 m
The dimensions are
2.5 m
One can of paint covers 3.5 m2. Each can of
paint costs 15.25. What is his total cost
including 13 GST and PST?
3.1 m
1.5 m
3
a) Determine the total area
2.3 m
A1
Atotal A1 A2
2.5 m
A l x w l x w
A 2.32.5 3.11.5
A2
3.1 m
A 5.75 4.65
1.5 m
A 10.4 m2
4
b) If one can of paint can cover 3.5 m2, how many
cans of paint will he need?
2.3 m
10.4 m2
2.5 m
Number of cans 2.97
3.1 m
He needs 3 cans of paint.
1.5 m
5
c) If one can of paint costs 15.25, what is his
total cost including 13 GST and PST?
2.3 m
10.4 m2
2.5 m
Paint cost 3 15.25 45.75
Taxes 0.13 45.75 5.95
3.1 m
Total cost 51.70
1.5 m
6

• Reflect
• In what other way might the area have been found?

• Why is this way of splitting the area less
  convenient than our original way?

We have to calculate side lengths that are not
given, and this introduces more sources of error.
7
What short-cut could be used to determine the
after-tax cost?
We had Paint cost 3 13.25 45.75 Taxes
0.15 45.75 5.95 Total cost
51.70
This calculation can be done all at once
The cost plus 13 of that cost is represented by
(10.13)
cost
A multiplier of 1.15 yields an increase of 13
What multiplier yields an increase of 20?
Of 35?
1.2
1.35