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Sat, 28 May 2022
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How do subtraction and division work in calcudoku?

It can often be a little confusing to see how subtraction and division work in a calcudoku puzzle compared to ordinary killer sudoku.

The reason for this is that the order matters in the way it does not with addition or multiplication.

We know that 4 x 5 = 5 x 4 and that 4 + 5 = 5 + 4

However, we also know that 9/1 is not the same as 1/9, and similarly that 2 - 5 is not the same as 5 - 2.

The way this is tackled in calcudoku is to ensure that you always start with the largest number, and then subtract or divide the other number(s) from it.

Thus if you had 9 and 1 in a subtraction region, you would always perform the calculation 9 - 1 to get a total of 8-.

Interestingly some calcudoku puzzles (you may know these as kenken TM or hitoshii TM which are trademarks) only allow subtraction and division regions to be of size two. There is no actual reason for this as once you have set the rule that you simply subtract or divide from the largest number in the region then there is no reason not to have subtraction or division regions larger than this.


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