In how many ways can 11 people stand in a row if two particular people must stand next to each other?
Answer and explanation
Correct answer: C.
- Step 1: Treat the pair as one block: units can be arranged in ways.
- Step 2: The pair can be ordered in 2 ways: .
Answer
.
Why not the others: : The restriction was ignored. : The two neighbours can also swap places. : The pair was not treated as a single block.
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