Answer:
29 books ; 5 bookshelfs
Step-by-step explanation:
Solving logically ;
Prime numbers between 21 and 30 = 23, 29
Hence, number of books Fernando has is either 23 or 29
Taking 4 away from the number of books, he'll be able to arrange same number of books on each of his book shelve;
From the statement, we can conclude that :
Subtracting 4 from the number of books Fernando has should give a perfect square
If 23 books
23 - 4 = 19 ; 19 isn't a perfect square
If 29 books :
29 - 4 = 25
Hence, to place the same Number of books on each shelf :
Sqrt(25) = 5
Hence, number of bookshelf = 5
