mAtboisLim
Member
Probability: Not mutually exclusive events. Please help.
The formula for two not mutually exclusive events is:
P(A or B) = P(A) + P(B) - P(A and B)
For the majority of questions involving not mutually exclusive events, in the P(A and B) part I was able to multiply the probabilities of A and B i.e {P(A) x P(B)} and subtract that from the sum of P(A) and P(B) to get a right answer for P(A or B).
However, for a question such as the following:
"From the integers 1 to 11, one is chosen at random. What is the probability that it is less than 9 or divisible by 4"
The multiplication gave me that 1/11 events can be counted twice, rather than the actual 2/11 which is obtained through a venn diagram.
Is there a set rule which will tell you where multiplication to find the intersection will not work? Or should I just abandon this and do it the long way?
Thanks in advance.
The formula for two not mutually exclusive events is:
P(A or B) = P(A) + P(B) - P(A and B)
For the majority of questions involving not mutually exclusive events, in the P(A and B) part I was able to multiply the probabilities of A and B i.e {P(A) x P(B)} and subtract that from the sum of P(A) and P(B) to get a right answer for P(A or B).
However, for a question such as the following:
"From the integers 1 to 11, one is chosen at random. What is the probability that it is less than 9 or divisible by 4"
The multiplication gave me that 1/11 events can be counted twice, rather than the actual 2/11 which is obtained through a venn diagram.
Is there a set rule which will tell you where multiplication to find the intersection will not work? Or should I just abandon this and do it the long way?
Thanks in advance.
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