P(B|A)
×
=
P(A)
P(A) P(B|A)
×
s
s+t
s+t+u+v
s+t
s+t+u+v
s
=
u
v
s
t
A
notA
B
notB
u
v
s
t
B
notB
×
u
v
s
t
B
notB
=