Here you will find: Puzzle Page Cross Sum January 20 2020 Answers. Let me explain how to play Cross Sum. Cross Sum is a mathematical puzzle where you must enter each of the numbers 1-9 in a grid to simultaneously satisfy six different sums. So how it works: use the number clues in the row and columns and deduce which numbers go in which squares. Only the numbers 1-9 can be used and can each be used once. Please note that the operations in each sum (+,-,×, ÷) are always applied left-to-right or top-to-bottom, rather than in the normal order of operator precedence.