(1) According to the meaning of the question, the frequency of [90, 100] group is 50-(2+3+14+15+12+4) = 4.

Make the following frequency distribution table:

? Scores? Frequency? Frequency [40,50]? 2 ? 125[50,60) ? 3 ? 350[60,70) ? 14 ? 725[70,80) ? 15 ? 3 10

[80,90) ? 12 ? 625[90, 100] ? 4 ? 225 (2) From (1), it can be seen that the number of students in [85 100] is 122+4= 10.

Then the proportion of students with grades above 85 is P 1= 1050=20%.

(3) Two students with [40,50] are A and A, and four students with [90, 100] are 1, 2,3 and b,

Then, the selected cases are (1, 2, a), (1, 2, a), (1, 3, a), (1, b, a).

(2, 3, a), (2, 3, a), (2, b, a), (2, b, a), (3, b, a), * * 12;

Among them, there are three situations in which two students, A and B, happen to be in the same group.

Then the probability that students A and B are arranged in the same group is P2 = 3 12 = 14.