Mutually exclusive stats homework

  • Thread starter daewoo
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  • #1
daewoo
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Homework Statement


Suppose that P(A) = 0.8 and P(A or B) = 0.9 , determine P(B) If
a) A and B are independent
b) A and B are mutually exclusive


Homework Equations


for Independence P(A and B) = P(A) x P(B)
for Mutually Exclusive P(A or B) = P(A) + P(B)


The Attempt at a Solution


for A) just by the formula i can say that P(A and B) = P(A) x P(B)
but i don't see still how i can find P(B), the P(A or B) part is really confusing to me.
 

Answers and Replies

  • #2
HallsofIvy
Science Advisor
Homework Helper
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For not mutually exclusive, part (A), p(A or B)= P(A)+ P(B)- P(A and B). Put the values into both that AND P(A and B)= P(A)xP(B).
 
  • #3
daewoo
25
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hm thanks, but how do you find out what P(B) alone is because i can't use that formula anyways.
 
  • #4
HallsofIvy
Science Advisor
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You can't use WHAT formula? And why not?
 

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