The law of total Probability is used to find the Probability of some event when we don’t know the probability of itself but we do know the probabilities , , , form a Partition of the Sample Space.
It states:
The law of total Probability is used to find the Probability of some event A when we don’t know the probability of A itself but we do know the probabilities B1, B2, B3, ... form a Partition of the Sample Space.
It states:
P(A)=∑iNP(A∣Bi)P(Bi)