Sudoku variant · rules and tips

XV Pairs

A V between two cells means they sum to 5. An X means they sum to 10. The letters are simply Roman numerals, proof that the Romans had opinions about Sudoku long before it existed.

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Professor Cryptic, the owl who teaches in the app
Professor Cryptic explains the rule

The Professor's tips

How do you solve XV Pairs?

01 / Warm up

Start on a 4 by 4 grid

  • With digits 1 to 4, a V admits 1 and 4, or 2 and 3. Two options per marker, and no others.
  • An X cannot appear on this grid at all. The largest sum available is 3 plus 4, which is 7, so you will meet only V markers here.
  • Where two V markers share a cell, that one digit must satisfy both sums at once. All three cells are bound together.
02 / Level up

Then try a 6 by 6 grid

  • A V admits 1 and 4, or 2 and 3. An X admits 4 and 6, since 5 and 5 would repeat a digit and the ordinary rules forbid it.
  • An X on a 6 by 6 grid therefore almost always means 4 and 6, which narrows both cells to a single pair.
  • Markers in the same row or column compete. If one V takes 1 and 4, no other V in that row may use either digit.
  • A marker sitting on a box boundary is especially valuable, because it links cells that belong to different regions.

The rule, drawn

What does XV Pairs look like?

  1. XV Pairs rule illustration, step 1 of 3
  2. XV Pairs rule illustration, step 2 of 3
  3. XV Pairs rule illustration, step 3 of 3

Start with a single square

Where can you play XV Pairs?

XV Pairs is one of the 17 variants in Cryptic, each with a lesson and unlimited puzzles.

Get it onGoogle PlayPlay on the web