SOLUTION: how many ways can 8 students in an examination hall be seated in a row if .the best friends dan and eben must seat together

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Question 1070266: how many ways can 8 students in an examination hall be seated in a row if .the best friends dan and eben must seat together
Answer by ikleyn(52800) About Me  (Show Source):
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The answer is 2*7! = 10080 ways.

7! accounts for permutations of 7 objects when you consider D an E as one entity.

The factor 2 accounts for the fact that in every permutations of 7 objects the entity DE can also go as ED.