Probability - calculation rules

Remember

The probability $P(E)$ for the occurrence of an event $E$ must always be between 0 and 1.

Hint

$P(E)=1$ is a sure event.

$P(E)=0$ is an impossible event.

Sum rule

The probability of an event $E$ corresponds to the sum of all its elementary events $e_1$ to $e_k$.

$P(E)=P(e_1)+P(e_2)$ $+...+P(e_k)$

Complementary event

The complementary event $E^c$ or $E'$ is the set of all results that $E$ does not contain.
$E^{c}$ occurs at the exact moment when $E$ does not occur.

The sum of the probability of an event and that of its complementary event equals always 1:

$P(E)+P(E^c)=1$

This also means:

$P(E^c)=1-P(E)$