A denotes event that present was hidden by mom. B denotes event that present was hidden by dad. E denotes event that present was hidden upstairs. F denotes event that present was hidden downstairs.
P(A)=.6 P(B)=.4 P(E|A)=.7 P(F|A).3 P(E|B)=.5 P(F|B)=.5
Find P(E)
Can you explain why the answer is: P(E) = P(A)P(E|A)+P(B)P(E|B) = (.6)(.7)+(.4)(.5) = .42 +.2 = .62