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Bayes' rule

P(A|B) = P(B|A) P(A) / P(B)

P(Getting Ace | Select a Spade) = P (Selecting a spade | Getting Ace) P(Getting Ace) / P(Getting a Spade)

P(Getting Ace) = 4/52 = 1/13

P(Getting a Spade) = 13/52 = 1/4

P(Selecting a spade | Getting Ace) = 1/4

P(Getting Ace | Select a Spade) = (1/4 . 1/13) / (1/4) = 1/13