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Number lock

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

All the numbers together make 15.Position 1 holds a number greater than 7.Position 2 holds an even number.Position 3 holds a number smaller than 2.816213
All the numbers together make 20.Position 1 holds a number greater than 8.Position 2 holds an even number.Position 3 holds a number smaller than 5.918233
All the numbers together make 16.Position 1 holds a number greater than 7.Position 2 holds an even number.Position 3 holds a number smaller than 2.916213

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.

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