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Mathematics in the mid-term exam of senior three.
Solution: The frequency distribution table of (1) samples is as follows:

(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.