By definition of conditional probability,
P(B | A) = P(A ∩ B)/P(A) = (13/25) / (13/20) = 20/25 = 4/5
The resulting equation 75 = 75 is an identity; this tells that the two equations of the system are equivalent, this is they both represent the same function. So, Lian can conclude that (option c) both gyms charge the same monthly rate and the same membership fee<span>.</span>
