Re: Plz
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a.if a night team includes 3 policemen, how many different teams are possible to have??
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C(20,3) = 1140
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b.if the policemen are ranked 1,2,...,20 in order of doing well, how many of these teams will not have the beat policemen??
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C(19,3) = 969
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c.How many the teams will have at least 1 of the best 10 policemen??
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C(20,3) - C(10,3) = 1020
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d.if one of these teams is selected at random to work in a particular night, what is the possibliy that the best policeman will not work that night??
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I'm not exactly sure what you're getting at with this. Is this assuming they were divided up into 7 teams (6 teams of 3 and 1 team of 2), or out of the 1140 possible teams?
I'll assume 1140 possible teams:
C(19,3)/C(20,3) = 85%, or just the obvious 17/20.
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