Set Square
A combination of simple arithmetic and logic are needed to solve this numerical grid puzzle.
The advantage of the grid is that it seems to turn the puzzle into a problem-solving exercise: the answers are known, the job is to work out which digits are required to provide them. If the same sums were written in a straight left-to-right format, it would occur to mathematicians that the rule of BODMAS ought certainly to apply, but this rule (Brackets, Order, Division, Multiplication, Addition, Subtraction) is not in fact used for this puzzle.
