Let $y_1$ , $y_2$ , $y_3$ ,..... $y_n$ be $n$ observations. Let ${w_i} = l{y_i} + k\,\,\forall \,\,i = 1,2,3.....,n,$ where $l$ , $k$ are constants. If the mean of  $y_i's$ is  is $48$ and their standard deviation is $12$ , then mean of $w_i's$ is $55$ and standard deviation of $w_i's$  is $15$ , then values of $l$ and $k$ should be

  • A

    $l = 2.5, k = 5$

  • B

    $l = 1.25, k = 5$

  • C

    $l = 1.25, k = -5$

  • D

    $l = 2.5, k = -5$

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