Four out of six people go to Paris, London, Sydney and Moscow. Each city requires one person to go, and each person only goes to one city.

According to the meaning of the question, according to the arrangement formula, four people from six people were selected to visit four cities respectively, and there was a different situation of 6 4 = 360.

Among them, A 5 3 =60 visits to Paris and B 53 = 60 visits to Paris.

So among the six people, if A and B don't go to Paris, there are 360-60-60=240 different options.

So among the six people, the probability that A and B will not go to Paris is P= 240 360 = 2 3.

So the answer is: 2 3.