There was a book that told average scenes and how to divide them up as you write.
uuhm... I can't remember which book it was though. I do remember who wrote it, and that I own the book; since I own three books by that author, that narrows it down to one of three books.
I think it was
this book--- I'm almost certain it was that one because that was the first of her books I bought, and I was thinking it was the first one I read that had like three chapters devoted to how many scenes you should put in each chapter of your book; but it could have been
this one; not sure, I bought this one a few weeks after the other one, and ended up reading both of them at the same time... they kind of went together almost like a volume one and two, and that's why I'm having a hard time remembering what info was in what book.

After I read those two books, I went out and bought a third book, which is a lot likke the first two, but not really the same, so I'm thinking it was not
this one, but than again it could be.
I know those books are screenwriting books, but they were actually recommended to me by my editor, who said he tells all of his authors to read them before doing the final editing of their novels. He said when authors used them as guides for editing their drafts, that they always ended up with better novels. All I can say is after reading them, they changed the way I look at my drafts now.
oh, and also, I write sci-fi, and currently most sci-fi publishes are requesting 90,000 to 120,000 words.
I also write romance and most romance publishers are currently asking for 75,000 to 150,000 words, depending on which line you are submitting to. YA romance is usualy in the 75,000 to 90,000 range, while epic historicals are in the 130,000 to 150,000 range.
While I don't write them, (just love to reead them), murder mysteries seem to be in the 75,000 to 90,000 range.
hope that helps some.
Basiclly when I'm writing I don't worry about number of scenes, chapters, or words, rather I just worry about the story it self and let it end at the ammounts it ends at.