Take a look here and here

S

21 posts
• Page **2** of **2** • 1, **2**

If you look in row 2, you see that the only ones are in box 3 (columns 7,8,9 -- in this specific instance, columns 8 & 9 only). Since there has to be a one in row 2, then it must be one of those two. That would mean that you could exclude all the others in box 3. Hence, the one in r1c9 could be cancelled.

- Dusty Chalk
**Posts:**21**Joined:**15 August 2005

The question is why can we eliminate 1 in R1C9. You will note there are 1's in R2C8 and R2C9 and with no other 1's in R2 one of these squares must contain the 1 for box 3 therefore you can safely eliminate the 1 in R1C9 . This scenario is what is meant by "possibles locked to a row " . If you can establish a certain number is confined to one box in a row or column you can safely eliminate that number from all squares in the other rows and columns squares in that box . Clear as mud!

- Ianac
**Posts:**6**Joined:**07 August 2005

21 posts
• Page **2** of **2** • 1, **2**