Dependence

P(x1 = H) = 1/2 -> H:P(x2 = H |x1 = H) = 0.9
T:P(x2 = T |x1 = T) = 0.8
P(x2 = H) = 0.55
P(x2:h) = P(x2 = H| x1 = H)*P(x1 = h)+ P(x2=H | x1 = T)*P(x1= T)

P(Y) = Σi P(Y|X=i) P(x=i) :total probability