Calcudoku is similar to killer sudoku, but also requires you to use subtraction, division and multiplication whilst solving the puzzle. The other key difference is that numbers may repeat within a sum region, as long as it doesn't invalidate the rule that a number can only be placed once in each row and column of the puzzle (there are no box regions in calcudoku).

The best way to solve calcudoku is to look through the grid at the start for sum regions that have the least number of options. Typically regions of just two cells will have less options than larger regions, though this is by no means always the case.

With multiplication regions, look for combinations that only have one option. In the sample grid to the right (filled with the solution for those who are unfamiliar with the puzzle) you can see the very first combination is 5x from two cells. Well, this must be '1,5' in some order.

Because the possible divisions are quite restricted then you will often find that looking at these reaps instant rewards to as there may not be many valid combinations, or perhaps even only one from the start.

Sometimes you won't know exactly where a number is placed, but know it must go in one of two cells. Then sometimes you can use this to help eliminate options from the rest of the region. For instance, imagine in row two that whilst solving the puzzle you know that the second and third (purple) cells must contain 3,4 in some order. Then you can eliminate those numbers as options from the other 4 cells in that row. You will find using logic like this very useful whilst solving calcudoku puzzles.

Of course, the simplest rules are that if a number can only appear in one cell in a row/column it must go there, and equally if an individual cell only has one option, then that option must be placed in that cell.

But the best overall tip for calcudoku is simply to play lots of them, because in that way you soon start to learn the combinations that crop up time and again, and if your maths is a little rusty also take the time to learn the combinations that only have one option for each of the operations for regions of two or three cells: this is the biggest time saver of all whilst solving calcudoku puzzles.

Now it's time to have a go at using these, and your own, calcudoku solving methods by tackling our own Calcudoku Puzzles >>>