The rules of cross math
Cross math is a 5 × 5 grid of numbers where every row and every column is a complete math equation using +, −, × and ÷. Some digits are already filled in; your job is to work out the missing ones so that every line is true. Every puzzle has exactly one solution.
The six rules
- Fill every blank cell with a digit from 1 to 9.
- Every row is an equation: the first two digits combined with the operator must equal the result on the right.
- Every column is an equation the same way, read from top to bottom.
- Work strictly left to right (and top to bottom) — there is no multiplication-before-addition precedence.
- Division is always exact (no remainders), and every equation's result is a positive whole number.
- There is exactly one solution, reachable by logic and simple arithmetic.
How to read the grid
Each line reads: digit, operator, digit, equals sign, result — and the result is always a single digit, so all the arithmetic stays small. For example, a row that reads 4 + 2 = 6 is complete. A row with a blank, like 8 ÷ ? = 4, needs the digit 2.
Left to right, not school rules
This is the rule people miss most. In cross math there is no operator precedence: 2 + 3 × 4 means (2 + 3) × 4 = 20, not 14. Always read the whole line from left to right, and columns from top to bottom, before judging whether it works.
One more thing: crossing lines
Every blank belongs to two equations — its row and its column. A digit is only correct if it makes both lines true. This is what turns cross math into a puzzle rather than a list of sums.