Let $a_1, a_2, \ldots, a_{10}$ be $10$ observations such that $\sum_{k=1}^{10} a_k = 50$ and $\sum_{k < j} a_k a_j = 1100$. Then the standard deviation of $a_1, a_2, \ldots, a_{10}$ is equal to:

  • A
    $5$
  • B
    $\sqrt{5}$
  • C
    $10$
  • D
    $\sqrt{115}$

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