Introduction to Ratios

Learn how to compare quantities using ratios

1. What is a Ratio?

A ratio compares two or more quantities. We use the symbol : to write ratios.

There are 3 yellow balloons and 4 green balloons.

Each box represents 1 balloon

The ratio of yellow balloons to green balloons is 3 : 4

We read this as "3 to 4" or "3 is to 4"

To bake a cake, Xinyi uses 1 cup of sugar and 2 cups of flour.

Each box represents 1 cup

Ratio of sugar to flour = 1 : 2

Ratio of flour to sugar = 2 : 1

Notice: The ORDER matters! 1 : 2 is different from 2 : 1

Rafidah bought 4 oranges and 12 pears. We can put them in groups of 4 to find the ratio.

In groups of 4: 4 oranges make 1 group, 12 pears make 3 groups

Ratio of oranges to pears = 1 : 3

This means: The number of pears is 3 times the number of oranges!

A : B is NOT the same as B : A, unless the two quantities are equal.

Always read the question carefully to know which quantity comes first!

In a class, there are 5 boys and 7 girls.

Ratio of boys to girls:

5 : 7

Ratio of girls to boys:

7 : 5

The mass of a durian is 5 kg and the mass of a papaya is 2 kg.

Each unit = 1 kg

Part-to-Part: Durian to Papaya = 5 : 2

Part-to-Part: Papaya to Durian = 2 : 5

Part-to-Whole: Papaya to Total = 2 : 7 (since 5 + 2 = 7)

We can compare three quantities using a three-term ratio.

There are 6 hamsters, 5 rabbits, and 8 dogs.

Ratio of hamsters : rabbits : dogs = 6 : 5 : 8

✓ A ratio compares two or more quantities
✓ We use ":" to write ratios (e.g., 3 : 4)
✓ Order matters! A : B is different from B : A, unless the two quantities are equal
✓ A ratio does NOT always show the actual numbers: 4 oranges and 12 pears have the ratio 1 : 3
✓ Part-to-whole ratio: compare a part to the total