Mathematics - Permutation & Combination Question with Solution | TestHub

MathematicsPermutation & CombinationnPr & nCrMedium2 minQB

MathematicsMediumsingle choice

Let $S = {1, 2, 3, \dots n}$ . If X denote the set of all subsets of S containing exactly two elements, then the value of $\sum_{A \in X} (min A)$ is

Answer:

Solution:

$\sum_{A \in X} min (A) = 1 (n - 1) + 2 (n - 2) + \dots\dots + (n - 1) 1$

$\sum_{r = 1}^{n - 1} r (n - r) =^{n + 1} C_{3}$

Stream:JEESubject:MathematicsTopic:Permutation & CombinationSubtopic:nPr & nCr

⏱ 2mℹ️ Source: QB

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