Hm, I haven't gotten this far, either. My computer has had some issues, so I had to stop fairly early on and haven't had a chance to get back to it yet. Yes, I agree that "random" puzzles like this are a pain.
I really liked the puzzle towards the beginning, however, where you had to figure out how the victim was killed and then do the crime reenactment. It was hysterical watching poor Watson having to play the part of the victim.
I admit, however, that while I enjoy the puzzles, I do play these games mostly for the experience of "playing through a story." So I'm more likely to choose a story/plot based game over a puzzle based game. This game - so far - seems like it has a very nice balance between the two. I should really get back to it so I can lament over this random number puzzle right along with you.