Not to be confused with "Mambo No. 5," this is Booklet No. 5. Sorry, folks, probably before your time. Well, in any case, I always liked the booklet-style items card companies came up with. I dunno why, just think they are unique and you get to learn more than what you usually find on the back of a card.
Here is the checklist of booklets:
http://www.oldbaseball.com/refs/70story.html