Add three one-digit numbers

What you will learn

• Add three one-digit numbers

Models used: number sentences, stories, diagrams.

Before you start

• Add and subtract within 100

Add two groups, then one more

We have 2 blue counters, 3 green counters and 4 orange counters. How many altogether?

1. Each counter is one object. Join every coloured group once. The groups still waiting must be added too.

   Here are two blue counters, three green counters and four orange counters. We want to find how many there are altogether.

2. Each counter is one object. Join every coloured group once. The groups still waiting must be added too.

   Start with the two blue counters. Move them into our big group.

3. Each counter is one object. Join every coloured group once. The groups still waiting must be added too.

   Now add the three green counters. Two and three make five. The four orange counters are still waiting.

   2 + 3 = 5

4. Each counter is one object. Join every coloured group once. The groups still waiting must be added too.

   Add the four orange counters. Five and four make nine. We have used all three groups, so there are nine counters altogether.

   2 + 3 + 4 = 9

Worked example: A new example, together

Add 1 + 4 + 3.

1. Each counter is one object. Join every coloured group once. The groups still waiting must be added too.

   We have 1 blue counter, 4 green counters and 3 orange counters. We will use every group once.

2. Each counter is one object. Join every coloured group once. The groups still waiting must be added too.

   Join 1 blue counter and 4 green counters. Leave the orange group where it is for now.

   How many counters have we joined so far?

   5

3. Each counter is one object. Join every coloured group once. The groups still waiting must be added too.

   We have 5 so far. Now add 3 orange counters.

   How many counters are there altogether?

   8

4. Each counter is one object. Join every coloured group once. The groups still waiting must be added too.

   There are 8 counters. We joined the first two groups, then added the third. Nothing was left out.

   1 + 4 + 3 = 8

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
• add all three groups once
• 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.