How to play

The rules for SumGrid's four puzzles, plus a few tips to get you started. Every puzzle has exactly one solution, and you can always reach it by logic alone, without guessing.

Sudoku

The board is a 9×9 grid split into nine 3×3 boxes. Some cells already have a number.

• Fill every empty cell with a digit from 1 to 9.
• Each row, each column and each 3×3 box must contain every digit 1–9 exactly once.

Tips

• Look for singles. Pick a digit and scan a box: if only one cell in that box can hold it, that's where it goes.
• Use notes. Turn on Notes to pencil in the possible digits. When a cell is down to one candidate, fill it in.
• Pairs. If two cells in a row can only be 4 or 7, no other cell in that row can be 4 or 7.

Number Sums

Every cell starts with a digit. The numbers outside the grid are the targets for each row and column, and each coloured region has a small target in its corner.

• Keep or erase each digit.
• The digits you keep in a row must add up to that row's target; the same goes for every column and every coloured region.
• When a row or column is complete, its target turns solid blue.

Tips

• If a row's target equals the sum of all its digits, keep them all. If the target is 0, erase them all.
• A digit bigger than its row's target can never be kept, so erase it.
• Check rows, columns and regions together: a cell that must be kept for its column might settle its whole region.

Sum Sudoku (killer sudoku)

Sum Sudoku mixes Sudoku with sums. All the normal Sudoku rules apply, but the board starts almost empty. Instead, groups of cells are outlined by dashed cages, each with a small total.

• Every row, column and 3×3 box contains 1–9 exactly once.
• The digits in each cage add up to the cage's total.
• A digit can't repeat inside a cage.

Tips

• Small and big cages are gifts. A 2-cell cage of 3 must be 1+2; a 2-cell cage of 17 must be 8+9.
• The 45 rule. Every row, column and box adds up to 45. If cages almost cover a box, the leftover cell is 45 minus the cages' totals.

Kakuro

Kakuro is like a crossword with numbers. Clue tiles hold a total for the run of white cells to their right (across) or below them (down).

• Fill each white cell with a digit from 1 to 9.
• The digits in each run must add up to its clue.
• A digit can't repeat within a run.

Tips

• Learn a few "magic" sums: 3 in two cells is always 1+2, 4 is 1+3, 16 is 7+9 and 17 is 8+9.
• Where an across run and a down run meet, the digit must fit both. That crossing is usually where you start.

Controls and settings

• Select a cell by clicking or tapping it, then choose a digit on the number pad.
• On a computer you can use the keyboard: type 1–9, move with the arrow keys, erase with Backspace, N toggles notes, H gives a hint and Ctrl+Z undoes. In Number Sums, K and E switch between Keep and Erase.
• Notes switches between writing answers and pencil marks. Auto fills in all possible notes for you.
• Hint reveals one correct cell (three per puzzle). Undo and Erase work as you'd expect.
• Lives: with the instant mistake check on, you have three hearts per puzzle. Turn it off in Account if you prefer to check at the end.
• Daily set: one puzzle of each kind, new every day. Finish all four to keep your streak.
• Your progress is saved automatically in your browser (or on your phone). To move it, use Account → Back up & restore.

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