'Tell Me Why' series - need help

[[deleted user]]

Hi,

The author Arkady Leokum wrote some well-known books in one or more series "Tell Me Why". There's an original set of 5 books, without numbering in the book titles. Later, there's another set of five books, with numbering in the book titles - possibly the same content as earlier, possibly not. Still later, there's a set of three book, which seem to combine content from one or the other of the earlier sets.

https://www.goodreads.com/author/show...

Between the two sets with five books each, the number of pages in corresponding books (e.g., #1 in each set) seems to differ significantly.

I've looked at WorldCat, Amazon, the publisher, and other resources via Google. Unfortunately, it's hard to pin down the relationship between Leokum's different book sets. Are there any suggestions for how to research this relationship?

Thanks!

[Michele]

Looks like there are two different series:

https://www.goodreads.com/series/1229...
https://www.goodreads.com/series/1182...