How to Play XV Sudoku: X and V Rules Explained

Everything else is ordinary Sudoku. Because each mark names exactly one partner for a known digit, a single placement can ripple along a chain of marks very quickly.

XV Sudoku rules in 30 seconds

1Every row, column and 3×3 box contains 1–9 exactly once.
2Cells joined by an X add up to 10.
3Cells joined by a V add up to 5.
4In these puzzles, a missing mark is not a clue.

See it on a board

X joins neighbours that add up to 10, V joins neighbours that add up to 5. Notice the 5 sits beside no mark at all: it never can.

Watch: how to play XV Sudoku

Still not sure? Some puzzles click faster when you see them solved. This 21-minute video from Steven Scott shows XV Sudoku in action.

“XV Sudoku - Rules & Strategies” by Steven ScottWatch on YouTube

The six pairs

There are only two ways to make 5 from different digits: 1+4 and 2+3. There are four ways to make 10: 1+9, 2+8, 3+7 and 4+6. Every V is one of the first two pairs and every X is one of the other four, in either order.

Why 5 never touches a mark

Neighbouring cells always share a row or column, so they can't hold the same digit. That rules out 5 + 5 for an X, and nothing else pairs with 5 to make 5 or 10. So a cell touching any X or V can never be a 5, and a cell touching a V can only be 1, 2, 3 or 4.

No mark, no information

In these puzzles only some summing pairs are marked. Two neighbours with nothing between them may still add up to 5 or 10, so never rule a digit out because a mark is missing.

Worked example

1A 3 sits beside a V, so its partner is 5 − 3 = 2.
2That 2 has an X on its other side, so the next cell is 10 − 2 = 8.
3One given digit has solved two more cells along the chain.

XV Sudoku tips and strategies

Subtract, don't scan

The partner of a known digit is 5 minus it for a V and 10 minus it for an X.

Place the 5s early

5s can only go in cells with no mark at all, which is usually a short list.

V cells are small

A cell on a V is 1–4, so that row, column and box must find its 6, 7, 8 and 9 elsewhere.

Follow chains

In a V–X chain, fixing one end fixes every cell along it.

Common mistakes to avoid

Treating a missing mark as "these two don't add to 5 or 10".
Putting a 5 next to a mark.
Forgetting the pair can go either way round until something else decides it.

Play XV Sudoku in 10+ Number Puzzles

X and V marks sit between cells and stay visible under every highlight.
Auto Notes fills candidates that respect every mark around a cell.
The hardest levels use very few given digits, so the marks carry the puzzle.
You have 3 lives. A wrong digit costs one.
Five difficulty levels, each a ladder of stages from Easy to Genius.
Go online for free: ranked 1v1 duels, rooms where you race, co-op or play in teams, and tournaments.
27 more puzzle types in the same app, and online play never costs coins.