NS-007

Find the next number: 11, 21, 31, 41, 51, ?

Rule: The pattern alternates: +10, +10, +10, +10, ... so the next step is +10.

So the next number is 61.

• Picking the first pattern you see without checking it against all rows/columns.
• Ignoring the simplest rule (counts, rotations, alternations) and jumping to a complex story.
• Not testing your rule on the middle row/column (where many puzzles “break” bad rules).