Add four small numbers · extra practice

What you will learn

• Extend three-number addition by joining one more small group, with totals within 20

Models used: counters, number sentences, bar models.

Before you start

• Add three one-digit numbers

One more group

We have 2 blue, 3 green, 1 orange and 2 pink counters. How many altogether?

1. Here are four small groups. Each counter will be counted once.

   2 + 3 + 1 + 2

2. Join the blue and green groups first. The orange and pink groups are still waiting.

   2 + 3 = 5

3. Bring in the orange counter. The pink group is still waiting.

   5 + 1 = 6

4. Bring in the pink group. No group is waiting now.

   6 + 2 = 8

Worked example: Let’s join them together

There are 3 blue, 2 green, 2 orange and 1 pink counters. How many counters in all?

1. Start with the blue and green groups. Leave the other two groups where they are.

   How many counters are together so far?

   5

2. Now bring in the orange group. Keep the pink counter for the last step.

   How many counters are together now?

   7

3. Bring in the pink counter. All four colours are together.

   How many counters are there in all?

   8

4. We counted every group once. The four groups make one whole.

   3 + 2 + 2 + 1 = 8

Common mistakes to discuss

• Stop at a subtotal. Check that none of the four groups is still waiting.
• Count a group twice. Move each group once and keep its colour.

Check your understanding

• Join two groups first, then add each waiting group.
• Include every group once.

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.