Probability is the chance of an event occurring. For example when flipping a coin you have a 50% chance that it will land on heads and a 50% chance that it will land on tails since there are only two possibilities.
Conditional probability refers to when one event is dependent on another event occurring. It can also be written as the probability of an event B occurring after event A has already occurred. The notation for conditional probability is P(B|A). (Note: this does not mean B divided by A but probability of B after A)
When two events are dependent, the probability of them both occurring is:
P(A and B)=P(A)P(B|A)
So for example: 53% of residents have home owners insurance. Of them, 27% has auto-insurance. If a resident is selected at random, what is the probability they with have both insurances?
Let H stand for home owners insurance = 53% or 0.53
Let A stand for auto insurance = 27% or 0.27
P(H and P)=P(H)P(A/H)
=(0.53)(0.27)
= 0.1431
So the probability of residents have both home owners and auto insurance is 0.1431 or 14.31%
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If events A and B are statistically indepnedent, then the conditional probability of A, given that B has occurred is the same as the unconditional probability of A. In symbolic terms, Prob(A|B) = Prob(A).
The probability of event A occurring given event B has occurred is an example of conditional probability.
Tree diagram
A conditional event.
This is a conditional probability, given the card is red, what is the chance it is a heart. Since there are 2 red hearts, the probability if 1/2