The idea, step by step
Double means two equal copies
To double 7, join 7 and another 7. The answer is 14. Doubling does not mean adding 2; it means adding the same number to itself.
Half means one of two equal parts
Halving shares the whole equally into two parts. Half of 14 is 7 because 7 + 7 = 14. If you double a number and then halve the result, you return to the starting number.
A common trap
Saying half of 12 is 10 because halving means taking away 2.
Instead: Halving means splitting into two equal shares. The shares must join to make 12: 6 + 6.
See the thinking
Double a collection
A tray has 9 muffins. Another matching tray has 9. How many muffins?
- The two groups are equal.
- 9 + 9 = 18.
Halve a length
A 16 cm ribbon is cut into 2 equal pieces. How long is each?
- Find two equal lengths that total 16 cm.
- 8 + 8 = 16.
Check your understanding
What is double 8? What is half of that answer?
Show answer
16, then 8.
8 + 8 = 16; sharing 16 equally between two gives 8.
Your turn
6 questions · Work at your own pace.
Read the questions online
- Find double 4.
- Find double 10.
- Find half of 18.
- Share 14 marbles into 2 equal groups. How many in each?
- A number doubled is 12. What was the number?
- Is double 3 the same as 3 + 2? Explain.
Read the worked solutions
- Find double 4.
4 + 4 = 8.
8 - Find double 10.
10 + 10 = 20.
20 - Find half of 18.
9 + 9 = 18.
9 - Share 14 marbles into 2 equal groups. How many in each?
7 + 7 = 14.
7 marbles. - A number doubled is 12. What was the number?
6 + 6 = 12.
6 - Is double 3 the same as 3 + 2? Explain.
Doubling joins two copies of the original amount.
No. Double 3 is 6, while 3 + 2 is 5.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics
Equal groups; arrays; repeated addition; sharing/grouping; twos facts; doubling and halving.
Official curriculum source ↗