Skip to content
START WITH A QUESTION

What would you like to understand?

Find an answer. See the moment it becomes clear. Follow the idea further.

← Concept directory

Answers for “为什么交换 A 和 B 通常会改变答案?”

3 keyword matches

Understanding your question. You can explore the search results below now.

Find a method

↗

Conditioning on event B restricts the sample space to only the outcomes contained within B. Within this newly restricted space, the favorable outcomes for event A are located exclusively in the intersection of A and B (A∩BA \cap B).

Conditions: Event B has occurred.; We are calculating the conditional probability of A given B.

Meet the concept

↗

For a conditioning event with positive probability, the formula is P(A∣B)=P(A∩B)/P(B)P(A\mid B)=P(A\cap B)/P(B). On a Venn diagram, the overlap region (A∩BA \cap B) serves as the numerator, and the entire conditioning region (BB) serves as the denominator.

Conditions: The conditioning event B has a positive probability (P(B)>0P(B) > 0).

Understand why

↗

Swapping the events changes both the numerator and the denominator in the conditional probability formula. P(A∣B)P(A\mid B) uses P(A∩B)P(A \cap B) as the numerator and P(B)P(B) as the denominator, whereas P(B∣A)P(B\mid A) uses P(A∩B)P(A \cap B) as the numerator but P(A)P(A) as the denominator.

Conditions: Events A and B have different marginal probabilities (P(A)≠P(B)P(A) \neq P(B)).; Both events have positive probability.