Understand the idea.
Find the step from known neighbours
Use known neighbouring numbers to find the step before filling a gap. In , the first jump adds four. Adding four to twelve gives sixteen; adding four again must reach the shown twenty.
Work backwards when needed
A missing beginning needs a backward step. In , the shown jumps add five going forwards. Undo that change by subtracting five from seventeen. Then read the completed pattern forwards to check it.
See the method in action.
A missing middle
Fill the gap: 30, 27, □, 21.
Worked solution
- 1
Find the step from the known pair.
The shown first jump subtracts three.
- 2
Use that step to fill the gap.
One more equal backward jump gives the missing middle number.
- 3
Check the next number.
The proposed twenty-four also fits the jump on the other side of the gap.
24
A missing start
Fill the gap: □, 18, 20, 22.
Worked solution
- 1
Check the forward rule.
Both complete jumps add two.
- 2
Undo one jump to find the start.
The number before eighteen must be two smaller.
- 3
Check forwards from the filled gap.
Sixteen leads to the next shown number under the same rule.
16
Try it yourself.
Check your understanding
Fill the gap: 5, 10, □, 20.
Show answer & reasoning
15
The step adds five. Since and , fifteen fits both sides of the gap.
Keep practising
6 worksheet questions
Read the questions online
- Fill the gap: .
- Fill the gap: .
- Fill the gap: .
- Fill both gaps: .
- Fill the gap: .
- Rui puts 19 in . Show two checks.
Read the worked solutions
- Fill the gap: .
; .
6 - Fill the gap: .
; .
30 - Fill the gap: .
The rule is add 3, so .
8 - Fill both gaps: .
Add 5 at every step.
- Fill the gap: .
Subtract 4 at each step.
28 - Rui puts 19 in . Show two checks.
The missing value follows the same rule on both sides.
and .
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics
Constant increases/decreases; describing rules; missing terms; shape/number patterns.
Official curriculum source ↗