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Question
There are three copies each of 4 different books. In how many ways can they be arranged in a shelf?
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Solution
Total number of books = 12
∴ Required number of arrangements = Arrangements of 12 things of which each of the 4 different books has three copies =\[\frac{12!}{3!3!3!3!}\]=\[\frac{12!}{(3! )^4}\]
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