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!
