Hidden Single in a Run

When a digit can only go in one cell of a run, it goes there, even if that cell has other candidates.

Level 2 Single digit in a run Technique 05

Why it works

A run needs a particular set of digits. If exactly one partition fits, every digit of that partition must appear in the run.

So if only one empty cell can take a required digit, that cell is decided. The cell may look flexible, with several candidates, but the run is hungry for that digit and has nowhere else to put it.

How to spot it

1. Work out which digits the run still needs.
2. For each of those digits, count the empty cells that can take it.
3. If a digit has exactly one such cell, write it in.

Practice it

Open the app, choose a level that uses this technique, and ask the coach for the next step. Every hint links back to this guide.