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1.9 Properties of Probability

Key Properties:

Union of Two Events (A ∪ B):

  • Represents all outcomes in event A, event B, or both.
  • Venn Diagram: Union is the combined area of two circles (A and B), including the overlap.
  • Example: For movies KGF (event A) and Kantara (event B): image

  • Interpretation: 76% chance either or both movies are a hit.

Intersection of Two Events (A ∩ B):

  • Represents outcomes common to both events A and B.
  • Venn Diagram: Intersection is the overlapping area of two circles (A and B).
  • Example: image

  • Outcomes: {8, 9, 11, 12} with probabilities \( 0.08 + 0.02 + 0.06 + 0.02 \).

Addition Law:

  • Formula: [ P(A ∪ B) = P(A) + P(B) - P(A ∩ B) ]
  • Simplifies to \( P(A ∪ B) = P(A) + P(B) \) if A and B are mutually exclusive (no overlap).

Mutually Exclusive Events:

  • Two events are mutually exclusive if they cannot occur simultaneously.
  • Example: Tossing a coin results in either heads (A) or tails (B) but not both.
  • image

Basic Requirements for Probabilities:

  1. image for any event E.
  2. The sum of probabilities of all sample space outcomes = 1.

Applications:

  • Union: Probability that either or both events occur (e.g., a hit movie).
  • Intersection: Probability that both events occur (e.g., both movies are hits).
  • Mutual Exclusivity: Simplifies addition law when events have no overlap.
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