Question

in how many ways 3 math books,4 history books, 3 chemistry books and 2 bio books can be arranged on a shelf . so that all the books on the same subject are togather.

Answer 1

Books can be arranged in 4 factorial ways  = 24 ways.

Answer 2

Answer:

First we take books of a particular subject as one unit. Thus there are 4 units which can be arranged in 4! = 24 ways.

Now in each of arrangements, mathematics books can be arranged in 3! ways,\

history books in 4! ways

, chemistry books in 3! ways and

biology books in 2! ways.

Thus the total number of ways = 4! × 3! × 4! × 3! × 2! = 41472.