A) 9/19
B) 9/38
C) 9/35
D) none
Correct Answer: A
Solution :
[a] The number of ways in which 20 people can be divided into two equal groups is \[n(s)=\frac{20!}{10!10!2!}\] The number of ways in which 18 people can be divided into groups of 10 and 8 is \[n(A)=\frac{18!}{10!8!}\] \[\therefore P(E)=\frac{18!}{10!8!}\frac{10!10!2}{20!}=\frac{10\times 9\times 2}{20\times 19}=\frac{9}{19}\]
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