10 people are arranged in 2rows of 5 in order to take a photograph,find number of arrangements that can be made if two are next to each other.
answer:645120
f5數學題一問?
2011-09-11 8:07 pm
回答 (1)
2011-09-11 11:25 pm
✔ 最佳答案
Case 1 :The pair (2P2 arrangements) in the upper row , then choose 3 peoples out of 8 (8C3 ways) ,so there are 4! arrangements in the upper row , while 5! arrangements in the lower row , 2P2 * 8C3 * 4! * 5! = 322560 arrangements.Case 2 :
The pair in the lower row , similarly , 322560 arrangements.Answer : 322560 x 2 = 645120 arrangements.
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