Understand the idea.
Double means two equal copies
To double a number, join it to an equal copy of itself. Doubling seven means . Think of two matching collections: the second collection has seven objects, so doubling seven adds seven rather than adding two.
Half means one of two equal parts
To halve a whole, split it into two equal parts and take the amount in one part. Half of fourteen is seven because . Equal parts must join back to the whole; doubling and halving undo each other.
See the method in action.
Double a collection
A tray has 9 muffins. Another matching tray has 9. How many muffins?
Worked solution
- 1
Identify the two matching collections.
Both trays contain nine muffins, so the total is double nine.
- 2
Add the two equal amounts.
The two trays together contain eighteen muffins.
18 muffins.
Halve a length
A 16 cm ribbon is cut into 2 equal pieces. How long is each?
Worked solution
- 1
Share the total length into two equal parts.
Halving sixteen gives eight for each of the two pieces.
- 2
Check that the two lengths rebuild the ribbon.
Two pieces of eight centimetres are equal and use the full ribbon.
8 cm each.
Try it yourself.
Check your understanding
What is double 8? What is half of that answer?
Show answer & reasoning
16, then 8.
Double eight is . Sharing sixteen into two equal parts gives , which returns to the starting number.
Keep practising
6 worksheet questions
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 ? Explain.
Read the worked solutions
- Find double 4.
.
8 - Find double 10.
.
20 - Find half of 18.
.
9 - Share 14 marbles into 2 equal groups. How many in each?
.
7 marbles. - A number doubled is 12. What was the number?
.
6 - Is double 3 the same as ? Explain.
Doubling joins two copies of the original amount.
No. Double 3 is 6, while 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 ↗