Let $n \geq 3$. A list of numbers $x_1, x, \ldots, x_n$ has mean $\mu$ and standard deviation $\sigma$. A new list of numbers $y_1, y_2, \ldots, y_n$ is made as follows $y_1=\frac{x_1+x_2}{2}, y_2=\frac{x_1+x_2}{2}$ and $y_j=x_j$ for $j=3,4, \ldots, n$.

The mean and the standard deviation of the new list are $\hat{\mu}$ and $\hat{\sigma}$. Then, which of the following is necessarily true?

  • [KVPY 2014]
  • A

    $\mu=\hat{\mu}$ and $\sigma \leq \hat{\sigma}$

  • B

    $\mu=\hat{\mu}$ and $\sigma \geq \hat{\sigma}$

  • C

    $\sigma=\hat{\sigma}$

  • D

    $\mu \neq \hat{\mu}$

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