How to Solve Number Cross: Sum Puzzle Strategy
Number Cross is a sum puzzle: fill each white cell with a digit from 1 to 9 so every run adds up to its clue, with no digit repeated in a run. Every grid has exactly one solution, so it can always be solved by logic. Learning a few number combinations makes it far easier.
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Learn the fixed combinations
Some totals can only be made one way. In two cells, 3 is always 1 and 2, 4 is 1 and 3, 16 is 7 and 9, and 17 is 8 and 9. In three cells, 6 is 1, 2, 3 and 24 is 7, 8, 9. In four cells, 10 is 1, 2, 3, 4 and 30 is 6, 7, 8, 9. Look for these first.
Use crossing runs
Every white cell sits in one row run and one column run. The digit must fit both. If a two-cell row run of 3 needs a 1 or 2, and the two-cell column run through one of its cells totals 4, which needs a 1 or 3, the shared digit must be 1. Crossings are where most cells get solved.
Watch for repeats
No digit may appear twice in the same run. Once a run has a 5 in it, no other cell in that run can be 5. Our keypad helps: digits shown dimmed are already used in the selected row or column runs, so you can skip them immediately when choosing a digit.
Big and small totals
Very small and very large totals are the most useful because they allow few digits. A two-cell run of 15 must be 6 and 9 or 7 and 8, so it can never contain a 1, 2, 3, 4 or 5. Ruling out digits like this narrows a crossing cell down to one answer. Leave middle totals, like 10 in two cells, until later.
Save hints for the end
A hint fills the selected cell, or a random empty or wrong cell, with the right digit, but it lowers your score. Clues turn green when their run is complete and correct, which makes mistakes easy to spot. Solving a Medium grid in under three minutes or a Hard grid without hints earns an achievement.
Questions
- Can a digit repeat in a run?
- No. Each digit can appear only once in the same row or column run.
- Which clues should I start with?
- Short runs with very small or very large totals, like 3 or 17 in two cells, which have only one combination.
- How do I know a run is correct?
- Its clue turns green when the run is complete and adds up correctly.
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