Fill in blank cells with numbers 1-9 so each group sums to its clue
Start with groups that have the fewest possible combinations
For two-cell groups, a sum of 3 means 1+2, and a sum of 17 means 8+9
Adults who regularly solve number puzzles show significant improvements in arithmetic reasoning, working memory, and attention. Neuroimaging studies also confirm that constraint satisfaction tasks activate prefrontal executive functions.