I'll explain to you the second Intermediate tutorial puzzle.

#1CompassPosted 5/4/2010 1:15:12 PM
Original thread is archived: http://www.gamefaqs.com/boards/genmessage.php?board=931667&topic=45543005

Simple answer: because the 4s on either side CANNOT be in the middle row. If two out of the three 4s of that horizontal set of 9x9 grids are NOT in the middle, then the third one must be.