Define the sample space
Identify the event of interest
Count favorable outcomes
Count total possible outcomes
Use the probability formula: P(event) = favorable outcomes / total outcomes
Check that all outcomes are equally likely, if using simple counting
Use complements when easier: P(not event) = 1 – P(event)
Use addition for mutually exclusive events: P(A or B) = P(A) + P(B)
Use multiplication for independent events: P(A and B) = P(A) × P(B)
Use conditional probability when events depend on each other: P(A given B) = P(A and B) / P(B)
Simplify fractions or convert to decimals or percentages as needed
Verify that probabilities are between 0 and 1
Make sure all probabilities in a complete set add up to 1