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1998

JEE Main 1998 Mathematics question on Permutations and Combinations

If an=∑r=0n1nCra_n = \sum_{r=0}^{n} \frac{1}{{}^nC_r}, then ∑r=0nrnCr\sum_{r=0}^{n} \frac{r}{{}^nC_r} equals
  1. A.
    (n−1) an(n-1)\, a_n
  2. B.
    n ann\, a_n
  3. C.
    12 n an\frac{1}{2}\, n\, a_n
  4. D.
    None of these
Show answer

Correct option: C

[1998]

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