A ratio compares two quantities. If a bag holds 6 red counters and 4 blue counters, the ratio of red to blue is 6 to 4, written 6:4. The order matters: 'red to blue' puts the red count first, so 6:4 and 4:6 are not the same. A ratio compares one part with the other part, not a part with the whole group — the 4 is the number of blue counters, not the 10 counters altogether. You read the two counts straight off and write them in the order the question names them.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- ratio
- a comparison of two quantities, written a:b
- part-to-part
- comparing one group with another group, not with the total
- term
- one of the numbers in a ratio
Worked examples
6 red and 4 blue — ratio of red to blue?
- 1.Red first: 6.
- 2.Then blue: 4.
= 6:4
3 green and 7 yellow — ratio of green to yellow?
- 1.Green first: 3.
- 2.Then yellow: 7.
= 3:7
5 black and 2 white — ratio of black to white?
- 1.Black first: 5.
- 2.Then white: 2.
= 5:2
For parents
Method: Read the two counts in the order they are named.
What to say: Ask 'which colour is named first?' — that count goes at the front of the ratio.
Common mistakes:
- Writing the ratio the wrong way round (blue to red).
- Comparing one colour with the whole group (6:10) instead of with the other colour (6:4).