One technique relies on the fact that the product of every row and column is a fixed number. For example, in a 5x5 "Inshin no heya" puzzle, each row/column must have a product of 120. If, in any row/column of such a puzzle, there is a 4-cell 24 clue, then the remaining cell in the row/column must be 5 to satisfy this property. Looking at the middle column in the sample puzzle, the 40 in the middle column reveals that the other two cells in that column must multiply out to 3 and therefore must consist of a 1 and 3. Since 3 is not a factor of 4, the 1 must be in the top cell and 3 must be in the second cell. This technique can also be extended to multiple rows/columns.