How to play: Number cross
Nine digits, six sums. Rows and columns have to add up at the same time.
- Place the digits from 1 to 9 in the nine cells, each one only once.
- Every row is a sum worked from left to right, and every column another one worked from top to bottom. The result of each is at the end.
- Sums go in reading order, with no precedence for multiplication: in “7 − 3 × 9” you subtract first and multiply after, and it makes 36.
- Tap a cell and press a digit, or move with the arrow keys and type it. Digits already placed show crossed out on the keypad.
- As soon as a row or column has its three digits, the result tells you whether it adds up. Some days come with one or two digits already in place.
- When all six sums add up, the puzzle is solved. It is timed, and your best time is kept.
Frequently asked questions
- Why does “7 − 3 × 9” make 36 and not −20?
- Because in this puzzle the sums are worked in the order they are written, like on an old-fashioned calculator: 7 minus 3 is 4, and 4 times 9 is 36. That is how newspapers have always printed it and how it is solved in your head.
- Can a subtraction go negative, or a division leave a remainder?
- No. Every step of the solution gives a whole number and never drops below zero. If trying a digit gives you an inexact division or a negative, that digit does not go there.
- Is there only one solution?
- Yes, always. On days when the six sums are not enough to pin it down, one, two or three digits come already in place: just enough for the solution to be unique.
- When does the board change?
- At midnight, Spanish mainland time. There is a new one every day, the same for everyone.