A) \[1-\frac{2}{n}\]
B) \[\frac{2}{n-1}\]
C) \[1-\frac{1}{n}\]
D) None of these
Correct Answer: A
Solution :
Let there be n persons and \[(n-2)\] persons not selected are arranged in places stated above by stars and the selected 2 persons can be arranged at places stated by dots (dots are \[n-1\] in number) So the favourable ways are \[^{n-1}{{C}_{2}}\] and the total ways are \[^{n}{{C}_{2}}\], so \[\times \bullet \times \bullet \times \bullet \times \bullet \times \bullet \times \] \[P=\frac{^{n-1}{{C}_{2}}}{^{n}{{C}_{2}}}=\frac{(n-1)\,!\,2\,!\,(n-2)\,!}{(n-3)\,!\,2\,!\,n\,!}=\frac{n-2}{n}=1-\frac{2}{n}\].
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