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counting and probability intermediate
Problem
In how many ways can 8 people be seated in a row of chairs if three of the people, John, Wilma, and Paul, refuse to sit in three consecutive seats?
Solution
The number of all seating arrangements is . The number of seating arrangements in which John, Wilma and Paul sit next to each other is . We can arrive at by considering John, Wilma and Paul as one person, arranging the ``six'' people (the JWP super-person plus the 5 other people) first, then arranging John, Wilma and Paul. Thus the number of acceptable arrangements is
Final answer
36000