Pa intersection b intersection c formula. The above formula relating conditional probability and the probability of intersection gives us an easy way to tell if we are dealing with two independent events. Given pa 020 pb 070 pa and b 015. Given three sets a b and c the intersection is the set that contains elements or objects that belong to a b and to c at the same time.
So p o c 1. We define mathamath and mathbmath to be independent if mathpacap b papbmath. 1 in a survey of 200 students of a school it was found that 120 study mathematics 90 study physics and 70 study chemistry 40 study mathematics and physics 30 study physics and chemistry 50 study chemistry and mathematics.
Intersection is also commutative. The intersection of a b c and d for example is unambiguously written a b. The intersection corresponds to the shaded lens shaped region that lies within both ovals.
Intersection is an associative operation. This formula is particularly useful when finding the probability of an event directly is difficult. That is for any sets a b and c one has a b c a b c.
A visual representation of the intersection of events a and b in a sample space s is given in figure 34 the intersection of events. When pa and pb are added the probability of the intersection and is added twice. The goal will be to calculate the probability of the union of these three sets or p a u b u c.
2 n a b c n a b n a c n a b c problems on intersection of three sets. Pa or b pa pb pa and b example 2. It thus makes sense to talk about intersections of multiple sets.
We will extend the above ideas to the situation where we have three sets which we will denote a b and c. Definition of the union of three sets. The probability of the union of events a and b is denoted by pa b.
This only works if they are. In fact since the empty set is included in any set the intersection of the empty set with any set is the empty set. To compensate for that double addition the intersection needs to be subtracted.
The probability that events a or b occur is the probability of the union of a and b. We write a b c. What is the formula for pab if a and b are overlapping events.
Since events a and b are independent if pa b p a it follows from the above formula that events a and b are independent if and only if. The probability of the intersection of events a and b is denoted by pa b. P is for probability.