Question

fill in the blank.
$p(a) + p(\bar{a}) = 1$ is one way to express the ______.

$p(a) + p(\bar{a}) = 1$ is one way to express the dropdown with options: addition rule, classical probability approach, rule of complementary events, rare event rule.

Explanation:

• The addition rule in probability deals with the probability of the union of events, not this form.
• The classical probability approach is about equally likely outcomes (e.g., \( P(A)=\frac{\text{number of favorable outcomes}}{\text{total number of outcomes}} \)), not this equation.
• The rule of complementary events states that an event \( A \) and its complement \( \bar{A} \) (the event that \( A \) does not occur) are mutually exclusive and exhaustive, so their probabilities sum to 1 (\( P(A)+P(\bar{A}) = 1 \)).
• The rare event rule is about determining if an event is unusual, not related to this sum.

Answer:

rule of complementary events