Ratio and proportion
Ratio
A ratio compares one part to another part. We write it with the notation a : b, and the order matters.
Writing a ratio
1. Count each group. 2. Write the amounts in the order the question asks, separated by a colon (:). 3. Swapping the order gives a different ratio, so keep it in order.
Worked examples
Circles to squares
- A necklace has 3 circles for every 1 square.
- Write circles first, then squares.
Answer: The ratio of circles to squares is 3 : 1.
The order matters
- Now write the ratio of squares to circles for the same necklace.
- Squares first this time.
Answer: The ratio of squares to circles is 1 : 3.
Where you see this in real life
- Mixing paint, like 2 cans of yellow for every 1 can of blue.
- A bead pattern with 1 black bead for every 3 white beads.
- A recipe that uses ingredients in a fixed ratio.
Key words
- Ratio
- A comparison of one part to another, written a : b.
- Proportion
- A comparison of a part to the whole.