two quantities are in direct proportion if the graph of one quantity against the other quantity is a...
TRANSCRIPT
Two quantities are in direct proportion if the graph of one quantity against the other quantity is a straight line through the origin.
So if one quantity doubles then the other quantity doubles.
Number of apples sold
Cos
t of
app
les
($)
1 The cost of five apples is $3.25. What is the cost of eight apples?
5 apples cost $3.25
1 apple cost $3.25 ÷ 5 =
8 apples cost $0.65 × 8 =
$0.65
$5.20
2 The recipe is for making cakes. The mixture will make two cakes. Helen wants to make seven cakes. Calculate the amount of each ingredient needed.
RECIPE:
200 g butter
160 g sugar4 eggs
150 g self-raising
flour1 tsp vanilla
essence
RECIPE:
200 g butter
160 g sugar4 eggs
150 g self-raising
flour1 tsp vanilla
essence
BUTTER: (200 ÷ 2) × 7 = 700 g
SUGAR: (160 ÷ 2) × 7 = 560g
EGGS: (4 ÷ 2) × 7 = 14 eggs
SELF-RAISING FLOUR: (150 ÷ 2) × 7 = 525 g
VANILLA ESSENCE: (1 ÷ 2) × 7 = 3.5 tsp
Two quantities are in inverse proportion if one quantity increases at the same rate as the other quantity decreases.So if one quantity doubles the other quantity halves.
1 It takes two men six hours to paint a fence. How long would it take three men to paint the
same fence?
2 men take 6 hours
1 man will take 2 × 6 hours =
3 men will take 12 ÷ 3 hours =
12 hours
4 hours
CHIRP
BIRD SEED
CHIRP
BIRD SEED
2 A box of bird seed lasts 5 birds 15 days. How long would the same packet of bird seed
last 30 birds?
5 birds for 15 days
1 bird for 15 × 5 days =
30 birds for 75 ÷ 30 days =
75 days
2.5 days
The graph can be used to convert between UK pounds (£) and US dollars ($).
0 20 40 60 80 1000
80
120
160
200
40
UK pounds (£)
US
dol
lars
($)
a Use the graph to convert £70 to US dollars. £70 ≈ $116
b Use the graph to convert $60 to UK pounds. $60 ≈ £36