Naked Pairs/ Twins
Naked Pairs / TwinsIf there are two cells in a house (row, column or box) that have only 2 candidates, you can eliminate these 2 candidates from all the other cells in that house.
We have marked the pencil marks for row #8.
Take a look at R8C7 or R8C8, both in the same row and have only 2 candidates each.
It is certain that one of these cells has to be '2' and the other '6'. It's still unknown which is which, but it doesn't matter. These two cells have no other options.
This means that no other cells in this row can be '2' or '6'.
We can eliminate '2' and '6' from R8C8 and we see that R8C8 has only one candidate, so we can solve it.
End of LessonNext Lesson:
Intermediate Solving Techniques - Naked Triples
Intermediate Solving Techniques - Locked Candidates Type 2 (Claiming)