How many ways can 1 arrange on bookshelf 5 thick books,4 mediumpar sized books and 3 thin books so that the books of the same size remain together?

We have 5 think books , 4 medium books and 3 thin books to be
arranged of a shelf.

The books of the same thickness must be
arranged together.

To arrange the thick books we have 5*5 ways = 25
way

to arrange the medium books we have 4*4 ways =
16

To arrange the thin books we have 3*3 = 9
ways

Now the number of ways are:

25 +
16 + 9 = 50 ways

Since we have 3 groups of books( thick , medium,
and thin), then there are (2*3=6) ways to arrange on the
shelf

==> The number of ways are 6*50 = 300
ways