.
First, you can select 3 publishers from 5 publishers by ways.
Then you can can select 4 books from each of the 3 boxes, containing 25 different titles, by ways.
Compute the mentioned numbers in each of the two lines above, and then calculate their product.
I assume that the ordering of books in the display does not matter
(since the problem says nothing about it).
You do all calculations, following my instructions.
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On Combinations, see introductory lessons
- Introduction to Combinations
- PROOF of the formula on the number of Combinations
- Problems on Combinations
- OVERVIEW of lessons on Permutations and Combinations
in this site.
Also, you have this free of charge online textbook in ALGEBRA-II in this site
- ALGEBRA-II - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this online textbook under the topic "Combinatorics: Combinations and permutations".
Save the link to this textbook together with its description
Free of charge online textbook in ALGEBRA-II
https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson
into your archive and use when it is needed.