Addition law probability

May 31, 2022, 16:45 IST

Addition law probability

Definition :-The addition law of probability (sometimes referred to as the addition rule or sum rule), states that the probability that a or b will occur is the sum of the probabilities that a will happen and that b will happen, minus the probability that both a and b will happen. The addition rule is summarized by the formula:
P(A∪B) = P(A)+P(B)−P(A∩B)

Addition Rule for Disjoint Events
Suppose A and B are disjoint, their intersection is empty. Then the probability of their intersection is zero. In symbols:Addition law probability The addition law then simplifies to:Addition law probability The symbolAddition law probabilityrepresents the empty set, which indicates that in this A and B do not have any elements in common (they do not overlap).

Example 1 :-Suppose a card is drawn from a deck of 52 playing cards: what is the probability of getting a king or a queen?

Solution :-Let A represent the event that a king is drawn and B represent the event that a queen is drawn. These two events are disjoint, since there are no kings that are also queens. Thus:Addition law probability

Example 2 :-If you take out a single card from a regular pack of cards, what is probability that the card is either an ace or spade?

Solution :-
Let X be the event of picking an ace and Y be the event of picking a spade.Addition law probability
The two events are not mutually exclusive, as there is one favorable outcome in which the card can be both an ace and spade.Addition law probability

Talk to Our counsellor