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Examples
Submitted by gfj100 on Wed, 11/11/2009  10:07
Example 1
The probability of a student getting an A in this course is 0.25 (Not True!) and the probability of
getting a B is 0.30 (again Not True!). What is the probability of getting an A
or
a B? According
to
Rule 4.a
, P(A or B) = P(A) + P(B) = 0.25 + 0.30 = 0.55. In this example events A and B
are
mutually exclusive
since a student cannot get both an A and a B for a course, but instead can
only get one grade. Take a look at the Venn diagram example below:
Example 2
The probability of a student in this course getting an A is 0.25; the probability of being female is
0.60. What is the probability of getting an A
or
being female? .
......
Can't say? Well, we could add
probabilities in example 1 since the two events were mutually exclusive, but in this example
getting an A and being female may both occur. So we just cannot simply add the probability of
one event to the probability of the other event  if we did we would be counting twice the
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 Spring '11
 AndyRegards
 Probability

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