How do you add probabilities?

1 Answer
VSH
Dec 3, 2017

We can add two probabilities as long as the events are disjoint.

Explanation:

Suppose A and B are two events.

#\P(A \text{ or } B \text{ occurs})# = #P(A \cup B) = P(A) + P(B) + P(A \cap B)#

Here #P(A \cap B)# is the probability that the two events occur simultaneously. If these events are disjoint, #P(A\cap B)=0# and in that case we can add the probabilities.

For example: Suppose events #A# and #B# are disjoint, #P(A) = 0.1, P(B) = 0.2 #, then #P(A \cup B) = 0.1 + 0.2 = 0.3#

Related questions
See all questions in Addition Rule
Impact of this question
2513 views around the world
You can reuse this answer
Creative Commons License