_P(B⋂A)
P (A|B) = ^{__________________________}

          P(B)





where A & B are events
P(B)≠ 0
P(A) & P(B) are the probabilities of observing A & B independently

conditional probability

P(A|B) = the probability of observing A given B is true
P(B|A) = the probability of observing B given A is true