For each position write down which numbers are still possible.
Clues about a single position ("greater than 6") cross out many numbers there.
Clues about all positions together ("all the numbers make 12") fit at the end - use them to check which options are left.
Example
- 8, 6, 1
- 9, 8, 3
- 9, 6, 1
For parents
What does this exercise practice?
The number lock links properties of numbers (even, greater, digit sum) with systematic elimination.
Common pitfalls
"Greater than 6" also rules out the 6 itself. Counting the boundary in often produces two answers instead of one.
How to practice at home
Take a real combination lock from a bike and give each other clues about the code you set.