Simple Rules for the Computation of Probabilities

The Independent Multiplication Rule

Independent Multiplication Rule: First, write down the independent stages that form the event: "Event E Occurs" = "First Event E₁ Occurs, then Event E₂ Occurs, then Event E₃ Occurs…"

Then compute the probability for each stage event: Pr{E₁}, Pr{E₂}, Pr{E₃}, …

Then compute the product of the stage event probabilities:

Pr{E} = Pr{E₁}* Pr{E₂}* Pr{E₃}*… Pr{E_{last stage}}

The stage events are mutually independent if the occurrence of any one of the stage events is independent of the occurrence of any of the others.