If the number of arrangements of n-1 things taken from n different things is k times the number of arrangements of n-1 things taken from n things in which two things are identical then the value of k is
A
12
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B
2
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C
4
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D
none of these
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Solution
The correct option is A 2 Selection of n-1 things from n things is =nCn−1 =n =a And Selection of n-1 things from n things is if two are identical =12!.nCn−1 =n2 =b Therefore a=kb or k=ab =2