A discrete random variable has $P (X = x) = k x$ for $x = 1, 2, 3, 4$ . Find $E (X)$ .

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Treating the eight values $2, 4, 4, 4, 5, 5, 7, 9$ as a whole population, what is the standard deviation?
$X \sim B (10, 0.3)$ . Find $P (X = 2)$ to 4 decimal places.
$X \sim B (8, 0.5)$ . Find $P (X \geq 7)$ to 4 decimal places.
$X \sim B (40, 0.25)$ . What is $Var (X)$ ?
$X \sim N (50, 16)$ (variance 16). Find $P (X > 58)$ .
$X \sim N (100, 1 5^{2})$ . Find the value $k$ such that $P (X < k) = 0.9$ .