The first of the two samples in a group has $100$ items with mean $15$ and standard deviation $3 .$ If the whole group has $250$ items with mean $15.6$ and standard deviation $\sqrt{13.44}$, then the standard deviation of the second sample is:

  • [JEE MAIN 2021]
  • A

    $5$

  • B

    $8$

  • C

    $4$

  • D

    $6$

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