Probability - conditional.
Overview.
Conditional probability is the determination of the probability of an event happening given knowledge about a related event.
For example, we throw a six sided dice. The probability of throwing a 4 is simply 1/6. If however we determine the probability of throwing a 4 knowing that the result is an even number, the probability reduces to 1/3. In the latter situation, the probability IS CONDITIONAL on certain prior knowledge.