Practise: Incomplete sums
This Killer puzzle stalls at exactly the point where Incomplete sums is needed. Work it out yourself, or jump straight to that position.
Skip the obvious cells and start where the technique matters.
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
Choose a complete row, column, box, or a combination of them, with several cages crossing its edge. Add the fully contained cages and subtract their total from 45, 90 or 135. Then inspect the boundary cells and their cages.
Put it to use
Where you will meet it
Expert grids are the only place this pattern regularly decides the solve. Bring your notes.
Play ExpertStuck 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