Five different books are arranged on a shelf so that two particular books are next to each other. In how many ways can this be done?
Answer and explanation
Correct answer: C.
- Step 1: Treat the two particular books as one block: objects can be arranged in ways. Step 2. The two books can be ordered inside the block in ways. Step 3. Total: . **Answer: . Why not the others:** : This forgets the two orders inside the block. : This is , with no restriction. : is , which has no basis in the block argument.
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