Question

The number of ways in which 3 Mathematics, 4 Physics, 2 Chemistry books can be arranged in a shelf so that the books of each subject are kept together is
(A) 20180
(B) 42320
(C) 34560
(D) 38480​

Answer 1

All 4 physics, maths and 2 chemistry books are to be kept together. Therefore we will make 3 groups of physics chemistry and maths .

Now these groups can be arranged in 3! ways and among these groups, these books can be arranged internally as 4!(physics),3!(maths)and 2!(chemistry)

Therefore total number of arrangements = 3! × 4! × 3! × 2!= 1728 ways