Short lessons. Small discoveries. Sudoku at your own pace.
Read the rules and examples below, then try the interactive exercises above. Each lesson introduces a technique and lets you practise it.
Normal sudoku rules apply: 1–9 once in every row, column and box. Dashed cages add a rule: their digits must add up to the small total. A digit can never repeat within a cage, even when it crosses a box boundary.
A two-cell cage with total 4 must contain 1 and 3. The alternative 2 + 2 is ruled out because a digit cannot repeat within a cage. Use rows, columns and boxes to determine their order.
Every combination in the list has the correct sum and distinct digits. But whole combinations can still be ruled out: a digit already present in the cage's row cannot be used in any of its cells. Click combinations to eliminate them, just as in the game's Killer tools.
A two-cell cage with total 5 has combinations 1 + 4 and 2 + 3. If both cage cells are in a row that already contains 4, rule out 1 + 4, leaving 2 + 3.
When a cage is almost complete, subtract its filled digits from the cage total. A cage totalling 6 with digits 1 and 2 leaves 6 − 1 − 2 = 3.
A cage with total 6 already contains 1 and 2 and has one empty cell. That cell must be 6 − 1 − 2 = 3.
A combination tells you which digits a cage contains, but not where they go. Use rows, columns and boxes to determine the order. A digit already in a column cannot appear there again. Then fill the entire cage.
A cage has two cells and total 3. Its combination is 1 + 2. If one cell’s column already contains 1, that cell must be 2 and the other cell must be 1.
1 + 2 + … + 9 = 45. Every complete row, column and box therefore totals 45. If whole cages cover all but one cell, subtract their sums from 45 to find the missing digit. If they cover the entire region plus an extra cell, subtract 45 from the cage sums to find that extra digit.
Whole cages cover eight cells in a row and their totals add up to 41. The row totals 45, so its ninth cell is 45 − 41 = 4. In this example the cages must not extend outside the row.