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Maths for SG Primary Schools

Primary 6 maths · Ratio, rate & percentage · About 12 minutes

Interpret ratios of two or three quantities using whole numbers

Keep the quantity labels in order. Distinguish one part from the sum of all ratio parts.

Start the interactive lesson →Open practice activity

What you will learn

Models used: number sentences, stories, diagrams.

Before you start

Keep the quantities in the named order

There are 2 red counters, 3 blue counters and 1 green counter. How do we write their ratio?

  1. All the small boxes represent equally sized units, even when they belong to different rows.

    Count the red and blue groups first. In the order red to blue, their ratio is 2 to 3.

    Red : blue = 2 : 3

    The counts of equal units describe the comparison. Their actual size comes from a given quantity or total.

  2. All the small boxes represent equally sized units, even when they belong to different rows.

    Include the green group as the third quantity. Keep red first, blue second and green third.

    Red : blue : green = 2 : 3 : 1

    One unit must have the same value in every row. That lets us compare amounts by counting their units.

  3. All the small boxes represent equally sized units, even when they belong to different rows.

    The order matters. If we name blue before red, the first two numbers must change places too.

    Blue : red : green = 3 : 2 : 1

    One unit must have the same value in every row. That lets us compare amounts by counting their units.

What did the picture help us see?

The order matters. If we name blue before red, the first two numbers must change places too.

Worked example: A new example, together

For every 1 red counters there are 2 blue and 4 green. Write red:blue:green.

  1. All the small boxes represent equally sized units, even when they belong to different rows.

    Keep the quantity labels in order. Distinguish one part from the sum of all ratio parts.

    The order of ratio terms must match the order of the named amounts.

  2. All the small boxes represent equally sized units, even when they belong to different rows.

    Read the named order.

    One unit must have the same value in every row. That lets us compare amounts by counting their units.

    For every 1 red counters there are 2 blue and 4 green. Write red:blue:green.

    1:2:4

  3. All the small boxes represent equally sized units, even when they belong to different rows.

    Read the named order.

    One unit must have the same value in every row. That lets us compare amounts by counting their units.

  4. All the small boxes represent equally sized units, even when they belong to different rows.

    Record the counts in that order.

    One unit must have the same value in every row. That lets us compare amounts by counting their units.

  5. All the small boxes represent equally sized units, even when they belong to different rows.

    Red:Blue:Green = 1:2:4.

    One unit must have the same value in every row. That lets us compare amounts by counting their units.

  6. All the small boxes represent equally sized units, even when they belong to different rows.

    Check the result against the question we started with.

    The first term represents red, the second blue, and the third green.

    We found 1:2:4. The order of ratio terms must match the order of the named amounts.

Common mistakes to discuss

Check your understanding

Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.

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