Eleven books consisting of 5 Mathematics, 4 Physics and 2 Chemistry are placed on a shelf. The number of possible ways of arranging them on the assumption that the books of the same subject are all together, is

Since, the books consisting of 5 Mathematics, 4 Physics and 2 Chemistry can be put together of the same subject in 5!4!2! ways.
But these subject books can be arranged it self in 3! ways
.'. Required number of ways = 5!4!3!2!