There are 10 stations on a circular path. A train has to stop at 3 stations such that no two stations are adjacent. The number of such selections must be?
A
50
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B
84
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C
126
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D
None of these
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Solution
The correct option is A84 Ifno.twostationareadjacentthen9pointsAtrainhastostopat3stationsThenrequiredselectionis[hcr=n!(n−r)!r!]9|!3=91(9−3)!3!=84