Mathematics - Probability Question with Solution | TestHub

MathematicsProbabilityGeneral (Event SS, Definitions, Odd against/Favour)Medium2 minQB

MathematicsMediumsingle choice

From a group of n persons arranged in a circle, 3 persons are selected at random .If probability that no two adjacent persons are selected is $\frac{2}{7}$ then $n =$

Options:

Answer:

Solution:

$P$ (no two adjacent persons are selected) $= \frac{n ( n - 4 ) ( n - 5 ) /6}{n ( n - 1 ) ( n - 2 ) /6} = \frac{( n - 4 ) ( n - 5 )}{( n - 1 ) ( n - 2 )} = \frac{2}{7}$ $\Rightarrow 5 n^{2} - 57 n + 136 = 0 \Rightarrow n = 8$

Stream:JEESubject:MathematicsTopic:ProbabilitySubtopic:General (Event SS, Definitions, Odd against/Favour)

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