P(A or B) = P(A) + P(B) - P(A and B)
For independent events: P(A|B) = P(A)
For independent events: P(A and B) = P(A) x P(B)
Mutually exclusive: P(A and B) = 0
Probability of $Y$ happening given that $X$ has occurred (conditional probability)
$$ P(Y|X) = \frac{P(Y\cap X)}{P(X)} $$
$$ \mu' = \frac{\frac{\mu}{\sigma^2}+\frac{\nu}{r^2}}{\frac{1}{\sigma^2}+\frac{1}{r^2}}=\frac{r^2\mu + \sigma^2\nu}{r^2+\sigma^2} $$
$$ (\sigma^2)' = \frac{1}{\frac{1}{r^2} + \frac{1}{\sigma^2}} $$