Question

Why is this wrong in Sudoku? I know I can’t put any of the same number in the same row, column, or box with numbers 1-9. But this 3 in red is not breaking those rules. I’m new to sudoku so please help!

Answer 1

If you put the red 3 where it is, you would be forced to put another 3 on the top-left corner of the central-left square. This would violate the first column.

This implies that the 3 in the central square must be in the top-central place.