There are 7 math books, 9 science books and 5 literature books. Student has to select 2 books from each set.
This is a combination problem.
Number of ways to select 2 math books from 7 books = 7C2 = 21
Number of ways to select 2 science books from 9 books = 9C2 = 36
Number of ways to select 2 literature books from 5 books = 5C2 = 10
Total number of ways to select 2 books from each set = 21 x 36 x 10 = 7560 ways.
So there are 7560 ways to select 2 books from each set of seven math books, nine science books, and five literature books