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Question
How many different selections of 4 books can be made from 10 different books, if two particular books are never selected?
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Solution
Two particulars books are never selected from 10 books. So, 4 books need to be selected from 8 books.
Required number of ways if two particular books are never selected =\[{}^8 C_4 = \frac{8}{4} \times \frac{7}{3} \times \frac{6}{2} \times \frac{5}{1} = 70\]
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