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题库 / Prep2007E2-PS-66
From a group of 21 astronauts that includes 12 people with previous experience in space flight, a 3-person crew is to be selected so that exactly 1 person in the crew has previous experience in space flight. How many different crews of this type are possible?
432
594
864
1,330
7,980
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21 austr = 12 with exp + 9 without exp
U need to form a group of 3 from 2 without exp and 1 with exp
Number of combinations of 2 people from 9 without exp is
2C9=36
for each of these groups u have 12 austr with exp, so u have
36*12=432 different groups
-From beatthegmat