There are 7 Harry potter books and 5 books needs to be arranged.
One of the five place is filled by book "Harry Potter and The Chamber of Secrets" and remaining 4 places must be filled by remaining 6 books.
So number of ways are,
[tex]\begin{gathered} 1\cdot^6P_4=1\cdot\frac{6!}{(6-4)!} \\ =1\cdot\frac{6\cdot5\cdot4\cdot3\cdot2\cdot1}{2\cdot1} \\ =1\cdot6\cdot5\cdot4\cdot3 \\ =360 \end{gathered}[/tex]So there are 360 ways in which 5 of 7 Harry pooter book can be arranges such that " Harry Potter and The Chamber of Secrets" must included.
