IntermediatePractice

Practise: Rule of 45

This Killer puzzle stalls at exactly the point where Rule of 45 is needed. Work it out yourself, or jump straight to that position.

Skip the obvious cells and start where the technique matters.

Practice

Mistakes0Hints0Score2,000Time0:00

Your turn first

Spot the idea before the hint explains it

1. Look
2. Check
3. Proof

Look at the marked starting cell, cage outline and sum. Which digit or combination is forced, and what visible sum fact supports your idea?

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.

Read about Rule of 45 again All Killer techniques

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 Hard

Stuck 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.

Open the solver