Suppose S and T are mutually exclusive events. Find P(S or T) if P(S) = 1/3 and P(T) = 5/12?

Question

3/4
7/18
5/36

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Answer 1 · 2017-04-20T13:59:12

In an OR situation you may ADD

#P(SorT)=P(S)+P(T)=1/3+5/12=4/12+5/12=9/12=3/4#

Answer 2 · 2017-04-24T11:47:41

# P(S uu T) = 3/4 #

We use the following fundamental definition from Probability and Set Theory:

# P(A uu B) = P(A) + P(B) - P(A nn B) #

And if we apply this to our problem we have:

# P(S uu T) = P(S) + P(T) - P(S nn T) #
# " " = 1/3 + 5/12 - P(S nn T) #
# " " = 3/4 - P(S nn T) #

Now we are told that #S# and #T# are mutually exclusive, and so:

# P(S nn T) =0 #

Hence,

# P(S uu T) = 3/4 #