Column Reduction puzzles
Method explanation: The Column Reduction method is similar to the Check Columns method. To use the Column Reduction method, pick a column, and then pick a number that is missing from that column. Then, test that number in all unfilled cells in that column to see if it is a possibility. If all of the possible cells for the missing number are in the same box, cells in that box that are not in the column cannot contain that particular number, and that candidate can be eliminated as a possibility.
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Using the Column Reduction method, which number goes in cell A1?
Example:
