There are 135 people in a sport centre. 73 people use the gym. 59 people use the swimming pool. 31 people use the track. 19 peop
le use the gym and the pool. 9 people use the pool and the track. 16 people use the gym and the track. 4 people use all three facilities. Given that a randomly selected person uses the gym and the track, what is the probability they do not use the swimming pool?
16 - 4 = 12 people use the gym and the track and do not use the pool;
9 - 4 = 5 people use the pool and the track and do not use the gym;
19 - 4 = 15 people use the gym and the pool and do not use the track.
At least two facilities use 4 + 12 + 5 + 15 = 36 people, 4 of them use all three facilities. Thus, the probability that a randomly selected person which uses at least two facilities, uses all the facilities is
