What were the odds?

I have a lot of books with titles that begin "100 Years of . . . ."  But very few with titles involving 75 years.

So what were the odds I'd pull two books off the shelf (actually, one book off the table where I keep books I've never used before) that had these titles:

75 Years of America Reading
Three-Quarters of a Century at Washington

Someone else can calculate the actual odds, but the number of titles I have in my database with 75 or some variation thereof is three (the other one is "75 Years of Children's Book Week Posters", which I used two weeks ago.