Series of books I read in 1980. Must have yellow binding w/black letters. One book was completely Greek Mythology. The other books in the set are different topics and are fuzzy to me. Your closest solution is M129, wrong color/binding. The Young Folks Shelf Books also wrong color binding.
Stump the Bookseller
New format, same book stumper solving.
Is it possible you are thinking of the Ingri D’Aulaire books? The D’Aulaire Book of Greek Myths is perhaps the best known, and has a primarily yellow cover, but there are also ones on Trolls, Norse Myths, and Norse Gods and Giants.