Suppose that a hotel owner estimates the probability that a customer booking a hotel room pays in advance (C1) is 0.35 and their probability of paying after check-out (C2) is 0.65. The hotel is fully booked for one weekend by a golfers’convention. Market research suggests that 55% of payments in advance and 35% of payments at check-out are by sports club members. Calculate the probability that those attending the golf convention will pay in advance, by also briefly discussing the main feature of the theoretical aspects behind the probability calculation adopted.