A Hidden Pair is two cells that are part of the same group and contain the same two candidates which are not present in any other cells in the group. The two hidden pair cells should contain more than the two identical candidates. This means that we can remove all other candidates from the Hidden Pair cells other than the hidden candidates.
If the hidden pair candidates only appear twice in the group and only in these two cells, they must be the solutions for the cells. Therefore all other candidates in the two hidden pair cells can be elliminated.
7 and 4 form the hidden pair in Box 6.
5 and 6 form the hidden pair in Row 1.
4 and 9 form the hidden pair in Column 7.
If you tap on the following links on an iOS device which has the Sudoku Tutor app installed, it will launch the app and open the practice puzzle. Tap hint once the puzzle is open to see the strategy in action.Sample Puzzle 1 Sample Puzzle 2 Sample Puzzle 3