Conditional probability is the probability of some event A, given the occurrence of some other event B. This is denoted P(A|B) and is read “the probability of A, given B”. In other words, we are calculating probabilities conditional on knowing further information partway through the experiment.
A math teacher gave her class two tests. 30% of the class passed both tests and 45% of the class passed the first test. What percent of those who passed the first test also passed the second test?
Two-thirds or approximately 66.7% of the class passed the second test.