GMAT Exam Success Simplified: Comprehensive Guides for Testing Exams

P(E) = 1 - P(not E) 3rd Rule of Probability: Conditional Probability Conditional Probability: The probability of event A AND event B occurring is the probability of event A times the probability of event B, given that A has already occurred. P(A and B) = P(A) × P(B|A) 4th Rule of Probability: Probability of A OR B The probability of event A OR event B occurring is: the probability of event A occurring plus the probability of event B occurring minus the probability of both events occurring. P(A or B) = P(A) + P(B) - P(A and B) Probability of Multiple Events Rules: • A and B < A or B • A or B > Individual probabilities of A, B • P(A and B) = P(A) x P(B) ← "fewer options" • P(A or B) = P(A) + P(B) ← "more options" Indistinguishable Events (i.e., anagrams with repeating letters) To find the number of distinct permutations of a set of items with indistinguishable ("repeat") items, divide the factorial of the items in the set by the product of the factorials of the number of indistinguishable elements.