Alibrary has 11 books on chemistry, 11 books on maths and 11 books on physics. in how many ways can these books be arranged in groups of eleven?

Distributing the 33 books in groups of 11 will make it 3 groups . the first group can be selected in 33C11 ... the next 11 can be selected in 22C11 ways and the last group can be selected in 11C11 ways . If you calculate uptill now the answer will apparently seem to be option 1 . But since the 3 groups are indistinguishable, all the possible ways of arranging these three groups in the order of their selection is negated .. therefore we have to divide the answer by 3!