Question 11
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Four people sit in a row of 10 seats so that no two of them are next to each other. In how many ways?
- A 840 Correct
- B 5,040
- C 35
- D 210
Correct Answer: Option A
Seats with no two adjacent: (10 − 4 + 1)C4 = 7C4 = 35
Arrange the 4 people: 4! = 24
35 × 24 = 840
Trap: 35 forgets that the people are different.
Answer: 840
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