In how many ways, can 10 different books be arranged on a shelf so that a pair of books will be (a) always together and (b) never together?
Added by Robert S.
Step 1
We can treat this pair as a single item, so we have 9 items to arrange (8 individual books and 1 pair). There are 9! ways to arrange these 9 items. However, the pair of books can be arranged in 2! ways (since there are 2 books in the pair). So, the total number of Show more…
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