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Answers for “事件 E 和 F 的容斥原理公式是什么?”

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Meet the concept

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The inclusion-exclusion formula for two events states that the probability of their union is the sum of their individual probabilities minus the probability of their intersection: P(E∪F)=P(E)+P(F)−P(E∩F)P(E \cup F) = P(E) + P(F) - P(E \cap F).

Conditions: E and F are events in the same probability space.

Find a method

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The probability of the intersection is calculated by rearranging the inclusion-exclusion formula to P(E∩F)=P(E)+P(F)−P(E∪F)P(E \cap F) = P(E) + P(F) - P(E \cup F). This is done by adding the intersection term to both sides of the original formula and subtracting the union term from both sides.

Conditions: The probabilities of the two individual events and their union are known.

Find a method

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To solve for the intersection probability, substitute the classical probabilities (favorable outcomes divided by total outcomes) into the inclusion-exclusion formula, keep a common denominator during the algebraic steps, and isolate the unknown intersection term.

Conditions: The sample space is finite and all outcomes are equally likely.; The probabilities of the two individual events and their union are known.

Understand why

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We subtract the intersection because adding the individual probabilities P(E)P(E) and P(F)P(F) counts the overlapping region twice. Subtracting P(E∩F)P(E \cap F) once corrects this double-counting so that every outcome in the union is counted exactly once.

Conditions: E and F are overlapping events in a probability space.

Know when to use it

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The inclusion-exclusion principle should be used when considering two events that are allowed to have overlap, meaning they can occur together. It is not the relevant setup for mutually exclusive events, where the intersection is empty and the events cannot occur simultaneously.

Conditions: There are two events under consideration.; The events can occur together (their intersection is not empty).

Understand why

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A probability must be a number between 0 and 1 inclusive. A percent value, such as 10, represents a whole number and falls outside this valid range.

Conditions: The value is intended to represent a probability.

Meet the concept

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The union of two events, denoted E∪FE \cup F, means that at least one of the events occurs. It is an inclusive 'or', meaning it includes the case where both E and F happen simultaneously.

Conditions: E and F are events in a probability space.

Understand why

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It is recommended to delay fraction simplification because all terms in the equation share a common denominator. Keeping the fractions unsimplified makes the addition and subtraction steps much easier and less prone to arithmetic errors.

Conditions: All probability terms in the equation share the same denominator.