$A$ random variable $X$ has the following probability distribution:
$X=x$$1$$2$$3$$4$
$P(X=x)$$0.1$$0.2$$0.3$$0.4$

The mean and standard deviation of $X$ are respectively:

  • A
    $2$ and $3$
  • B
    $3$ and $1$
  • C
    $3$ and $\sqrt{2}$
  • D
    $2$ and $1$

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