1-2-1 and 1-2-2-1
Both are two 1-2 patterns side by side. In 1-2-1 the mines are under the 1s, in 1-2-2-1 under the 2s.
Read the line of numbers from each end as a 1-2 pattern: the 2 shows a mine, the 1 a safe cell. In 1-2-1 the two pairs point at the cells under the two 1s, so those are mines and the cell under the 2 is safe. In 1-2-2-1 they point at the cells under the two 2s.
How it works
A line of numbers along hidden cells. Read it from each end as a 1-2 pattern.
Your turn
Each board is a real position from a game. Tap or click to open; right-click, long-press or switch on Flag to place a flag. If you are not sure, take a hint: the first one only shows where to look.
Which hidden cells can you be sure of?
How the exercises were chosen
A computer checked every board: in what you see, no number on its own proves anything, and the only pairs of numbers that do are the 1-2 pairs of the line.