There are 6 Novels and 3 Dictionaries. There are to be made arrangements of books in a Shelf consisting of 4 Novels and 1 Dictionary, such that Dictionary is always in the middle.
I tried to do this by: There should be 2 novels to the left of dictionary and 2 to the right i.e. 6C2 and out of remaining 4C2, and dictionaries can be arranged as 3C1.
So total arrangements: 6C2 * 4C2 * 3C1 = 15*6*3 = 270? Is my reasoning correct? Can you tell me where I am wrong, Since the answer is incorrect. Thanks in advance
Select $1$ dictionary from $3$ in $^3C_1$ ways
Select $4$ novels from $6$ novels in $^6C_4$ ways
Since you chose $4$ novels from $6$, now you can arrange those $4$ novels in $4!$ ways.
Since the dictionary should be in middle $NNDNN$ is the arrangement
$$^6C_4\times^3C_1\times4!\times1!=1080\mbox{ ways.}$$