Once you attempt the question then PrepInsta explanation will be displayed.
: the 4 books to be together can be treated as 0ne set
So we have 1 set of books and remaining 8 books which makes total 9 books to be placed in shelf
(9-1)!
Now books can be arranged in total of 4 ways
(9-1)! * 4!
Now books can be placed in any direction so
(9-1)! * 4! /2
483, 840
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