ISBN strangeness

[Michael]

This book has an X instead of the last digit for the ISBN.
http://www.goodreads.com/book/show/39...
I tried looking on WorldCat to see what the right ISBN should be, but it had an X in the last place, too. Is it normal for some books to have letters instead of numbers in their ISBNs? I have never seen this before.

[rivka, Former Moderator]

Yes, for ISBN-10's approximately one book in ten will have an X in the final (check) digit.

[Michael]

Oh, ok. I'd just never seen that before. Thanks, rivka!

[rivka, Former Moderator]

ISBN-13's, OTOH, never have an X. It's one of the improvements to the newer system.