1. Direct Proportion Thursday, 18 April 2019
Unitary Methods
Direct Proportion
Thursday, 18 April 2019

2. Example
If 5 books cost £30, find the cost of 8 books
5 books = £30 30
1 book =
= £6 5
8 books =
6 x 8
= £48

3. Example
If 7 pens cost 63 pence, find the cost of 12 pens.
7 Pens = 63 63
1 pen =
9 pence 7
12 pens =
9 x 12
= 108 pence

4. Example
If 12 calculators cost £72, find the cost of 9 calculators.
12 Calculators = £72 72
1 Calculator = £6 12
9 Calculators =
6 x 9
= £54

5. Example
If a machine takes 20 seconds to make 8 components, how long will it take to make
16 components?
20 components?
(i) 16 components =
2 x 20
= 40 seconds
(ii) 8 components = 20 20
1 component =
= 2.5 8
20 components =
2.5 x 20
50 seconds

6. Example
A plane flies 50 km in 15 minutes.
a) How long will it take to fly 300 km?
b) How many kilometres will it fly in 24 minutes?
a) 50 km = 15 mins
b) 15 minutes = 50 km 15 50
1 km =
= 0.3
1 minute =
= 10/3 50 15
300km =
0.3 x 300
= 90 minutes
24 minutes =
10/3 x 24
= 80 km