... conditional probability into (2.7) and mul-tiplying by P (B) leads to the equationP (A ∩B) = P (A) ·P(B).An Introduction to StatisticalInference and Data AnalysisMichael W. Trosset1April 3, ... 4 ways to choose a ring for the left hand and, foreach such choice, there are three ways to choose a ring for the right hand.Hence, there are 4 ·3 = 12 ways to choose a ring for each hand. This ... The sum ofthese random variables, X1+X2, is evidently equivalent to the randomvariable Y .The primary reason that we construct a random variable, X, is to replacethe probability space...