A quad number has been entered in each of the small squares.
The four quad numbers at the corners of each sum number add up to that sum number.
There are no duplicate numbers within each sum’s four quad numbers.
Incorrect: The quad numbers
don’t add up to the sum.
Incorrect: There are
duplicate quad numbers.
Correct: The numbers add up
and there are no duplicates.
A typical Quadsum puzzle
The puzzle solved
Difficulty Level
The difficulty level of a Quadsum puzzle is controlled by various factors, including the size of the puzzle, the sum numbers chosen, the adjacencies of sum numbers, and seeding. These same factors are used to control the number of solutions. (Many puzzles have multiple correct solutions.)
