Use +, − and = correctly

What you will learn

• Use +, − and = correctly

Models used: number sentences, stories, diagrams.

Before you start

• Find the missing part

The equals sign says “the same amount”

The left side has 3 and 2 counters. The right side has 5.

1. The complete bar is the whole. Each labelled section is one part of it.

   The left side has 3 and 2 counters. The right side has 5.

   3 + 2 = 5

   An equation compares two amounts. A picture can show why those amounts match.

   5

   32

2. Matching bags hold the same amount. A level balance means both sides have equal value.

   Both sides describe five. The equals sign connects two names for the same amount.

   Equality is a relationship between both sides. Adding or removing the same amount on both sides keeps that relationship true.

   5 = 5 · balanced

3. The complete bar is the whole. Each labelled section is one part of it.

   We can write the sides the other way round. They still name the same amount.

   5 = 3 + 2

   5

   32

Worked example: A new example, together

What is 10 − 2?

1. Each counter stands for one object. Count each counter once to find how many there are.

   Start with 10 counters.

2. The picture starts with 10 counters. Crosses mark 2 taken away. Count only the counters without crosses to find what remains.

   Take away 2. Cross them out.

3. The picture starts with 10 counters. Crosses mark 2 taken away. Count only the counters without crosses to find what remains.

   Count what is left: 1, 2, … 8.

4. The picture starts with 10 counters. Crosses mark 2 taken away. Count only the counters without crosses to find what remains.

   Use the picture and the steps we have just followed to finish this question.

   What is 10 − 2?

   8

5. The picture starts with 10 counters. Crosses mark 2 taken away. Count only the counters without crosses to find what remains.

   So 10 − 2 = 8.

   10 − 2 = 8

6. Blue counters stayed. Orange counters are the 2 we put back. Together they restore our starting 10.

   Put back what we took away. Check: 8 + 2 = 10.

   8 + 2 = 10

   8

   2

Common mistakes to discuss

• “=” means an answer follows. The equals sign says the two sides have equal value. 3 + 2 = 5 and 5 = 3 + 2 are both correct, and 7 = 7 is a complete statement.

Check your understanding

• Use +, − and = correctly
• read an equation as a relationship between equal amounts
• 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.