Practise: Rule of 45
Each practice board contains one row, column or box whose fully contained cages leave exactly one cell. Find its missing share of 45 before opening the proof.
Add only the cages fully inside the marked unit. Subtract their total from 45 and place the result in the one remaining cell.
Your turn first
Which digit completes the total of 45?
- 1. Look
- 2. Check
- 3. Proof
Choose the highlighted row, column or box and identify the cages that lie fully inside it.
Example 1 of 4
How to spot it
Pick a row, column or box where cages mostly stay inside. Add the sums of the cages fully contained in it, then compare with 45. The difference is the total of the remaining cells.
Put it to use
Where you will meet it
Hard grids are built around moves like this one. That is where it earns its keep.
Play HardStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
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