(2) There are 6+4= 10 people whose estimated score is above 85.
Therefore, the proportion of students with estimated scores above 85 points is;
(3) [40, 50] There are two people, marked A and A respectively; There are four people in [90, 100], marked as B, B, C, D,
Then the "two gangs and one" group has the following 12 grouping methods: A B, A C, A D, A BC, ABD, ACD, AB, A B C, A B D, ABC, Abd, ACD,
Among them, there are three ways for students A and B to be in the same group: A, B, C, D,
So the probability that students A and B happen to be in the same group is.