Add three one-digit numbers

What you will learn

• Add three one-digit numbers

Models used: number sentences, stories, tables.

Before you start

• Add and subtract within 100

Choose a useful pair first

We want to join 6, 3 and 4 counters. Which two groups could make a ten?

1. Each counter stands for one object. The separate groups are parts; count all the groups to find the whole.

   We want to join 6, 3 and 4 counters. Which two groups could make a ten?

   Joining two groups gives a useful subtotal. The third group still belongs to the whole.

   6

   3

   4

2. Each dot stands for one object. A full row holds five; two full rows make ten.

   Join 6 and 4 first. That makes a full ten-frame.

   6 + 4 = 10

3. Each dot stands for one object. A full row holds five; two full rows make ten.

   The other 3 have not disappeared. Add them to our ten.

   6 + 3 + 4 = 13

Worked example: A new example, together

Add 1 + 4 + 3.

1. Three parts form one whole. Read each value with the heading above its column.

   Follow which groups have already been joined and which one is still waiting.

   Addition joins all three parts into a whole.

   Three parts form one whole

   First part	Second part	Third part
   1	4	3

2. Three parts form one whole. Read each value with the heading above its column.

   Choose two parts first: 1 + 4 = 5.

   Three parts form one whole

   First part	Second part	Third part
   1	4	3

   Add 1 + 4 + 3.

   8

3. Three parts form one whole. Read each value with the heading above its column.

   Choose two parts first: 1 + 4 = 5.

   Three parts form one whole

   First part	Second part	Third part
   1	4	3

4. Three parts form one whole. Read each value with the heading above its column.

   Join the third part: 5 + 3 = 8.

   Three parts form one whole

   First part	Second part	Third part
   1	4	3

5. Three parts form one whole. Read each value with the heading above its column.

   The order of joining these parts does not change their total.

   Three parts form one whole

   First part	Second part	Third part
   1	4	3

6. Three parts form one whole. Read each value with the heading above its column.

   Check the result against the question we started with.

   8 − 3 = 5.

   We found 8. Addition joins all three parts into a whole.

   Three parts form one whole

   First part	Second part	Third part
   1	4	3

Common mistakes to discuss

• Stopping after two numbers. Every group must be counted once. In 4 + 6 + 2, pairing 4 and 6 to make ten is a useful start, but the 2 still has to be added.

Check your understanding

• Add three one-digit numbers
• join three parts without omitting or repeating one
• check the answer against the original quantities and units

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.