The Equals Sign and Missing Numbers
What this lesson covers
- + means add and − means take away.
- = means both sides are the same amount.
- A number sentence can have a missing number to find.
- A number sentence can be true or false.
Three signs
- + means add. Join the groups together.
- − means take away.
- = means is the same as.
| Sign | Say it | Example |
|---|---|---|
| + | plus, add | 3 + 2 |
| − | minus, take away | 5 − 1 |
| = | is the same as | 3 + 2 = 5 |
Equals means balanced
- Think of a seesaw. It is level when both sides weigh the same.
- 3 + 2 = 5 is balanced. So is 5 = 3 + 2.
- 4 + 1 = 3 + 2 is balanced too: both sides are 5.
A missing number
- A number sentence with a gap is called an open number sentence.
- 4 + __ = 6 has a missing number.
- Ask: what makes both sides the same? 4 + 2 = 6, so it is 2.
Fill the gap
- Work out the side you can.
- Then make the other side match.
| Sentence | Known side | Missing number |
|---|---|---|
| 2 + 5 = 3 + __ | 2 + 5 = 7 | 4 |
| 6 + 2 = 4 + __ | 6 + 2 = 8 | 4 |
| 9 − 3 = __ + 1 | 9 − 3 = 6 | 5 |
| 8 − __ = 5 | 5 | 3 |
Try it: make it balance
True or false?
- Work out each side.
- Same amount: true. Different amounts: false.
| Sentence | Left | Right | True or false? |
|---|---|---|---|
| 7 − 5 = 6 − 4 | 2 | 2 | true |
| 3 + 4 = 8 | 7 | 8 | false |
| 5 + 1 = 4 + 2 | 6 | 6 | true |
| 9 − 2 = 8 − 3 | 7 | 5 | false |
Try it: true or false?
Common mistakes
- 2 + 5 = 3 + __, so the missing number is 7.Both sides must be 7. 3 + 4 = 7, so the missing number is 4.
- = means 'the answer comes next'.= means both sides are the same amount.
- 5 = 2 + 3 is wrong, because the answer comes first.It is true. Both sides are 5.
- 3 + 4 = 4 + 3 is false, because the numbers moved.It is true. Both sides are 7.
Your turn
1
2 + 5 = 3 + __
2
6 + __ = 9
3
True or false: 7 − 5 = 6 − 4
4
True or false: 4 + 3 = 8
5
8 − 2 = 4 + __
Show answer
1. 4 2. 3 3. True, both sides are 2 4. False, 4 + 3 = 7 5. 2
What to take away
- = means both sides are the same.
- Work out the side you know, then fill the gap.
- Check each side to decide true or false.
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