The basics of ratio

1. Ratio My bike’s fuel has
a ratio of
oil to petrol
1 : 25
Sounds
complicated

2. Using the simplest ratio to
describe different quantities.
Sue is explaining
how to use a ratio to
describe red and
green hearts.

3. Count the number of red and green hearts
4 RED and 8 GREEN
Record the numbers using headings like this
Red : Green
The :
4:8 says ‘to’

4. Try to write the ratio in its
simplest terms
Red : Green
4:8
Divide ÷
Divide ÷
2:4 by 2
by 2
1:2

5. The ratio of red to green is
Red : Green
1:2
This tells you that there
are 2 green hearts for
every red heart

6. Copy and complete this chart
Ratio Simplest terms
12 : 16
24 : 32
27 : 36
28 : 40

7. Copy and complete this chart
Ratio Simplest terms
12 : 16 3:4
24 : 32 3:4
27 : 36 3:4
28 : 40 7 : 10

8. Sharing a quantity into a given ratio
For example, share 36 into the ratio 2:7
First ADD the ratio 2 + 7 = 9
Second DIVIDE this answer into
the quantity to be shared 36 ÷ 9
=4
Third MULTIPLY the ratio by
this answer 2 X 4 : 7 X 4
This is the answer 8 : 28

9. To share into a given ratio, the things
to do are:
+ ÷ X
Share 32 into the the ratio 3 : 5
3+5=8 32 ÷ 8 = 4
3 X 4 = 12 : 5 X 4 = 20
Answer 12 : 20

10. Share these into the given ratio
Ratio Quantity Share
2:3 50
2:5 28
3:7 20
4:5 360
1:2:5 32

11. Share these into the given ratio
Ratio Quantity Share
2:3 50 20 : 30
2:5 28 8 : 20
3:7 20 6 : 14
4:5 360 160 : 200
1:2:5 32 4 : 8 : 20

12. Finding an unknown number
that fits a given ratio
Example – If the ratio of red beads black
beads is 3 : 5, how many black beads
will I need for 21 red beads?
Red : Black
3:5
21 : ?

13. First find the number that
you multiply 3 by to get 21
Red : Black
3:5
X7
21 : ?

14. Red : Black
3:5
X7 X7
21 : 42

15. Another Example
Red : Black
2 X 6 is
2:7 12 so you
multiply
7 by 6 to
X6 get the ?
12 : ?

16. Red :
Black
2: 7 X6
X6 12 : 42