From 6 different novels and 3 different dictionaries, 4 novels and 1 dictionary are to be selected and arranged in a row on a shelf so that the dictionary is always in the middle. Then the number of such arrangements is -

We're picking 5 books in total. The dictionary will be the middle book so let's look at that first.

There are 3 different dictionaries to pick from, and so the number of choices for that middle book is 3.

The remaining 4 spots for books will be chosen from a population of 6. We can use the permutation formula (P6,4=6!2!=6×5×4×3=360).

All told, there is 3×360=1080 ways to arrange the books.