Accordingly, it is estimated that the average score of this exam is 7 1. (3 points)

(2) [70,80] points (4 points) There are 12 people.

p = c 2 12c 240 = 1 1 130

Choose two students from these 40 students, and the probability that their grades are [70,80] is 1 1 130.

(iii) There are 65,438+00 students with [40,60] and 30 students with [60, 100], so the possible value of X is 0, 1 2 (8 points).

Then p (x = 0) = c 210c240 = 352p (x =1) = c130c = 513p (x = 2) = c240.

So the distribution table of X is (12 points).

Mathematical expectation ex = 0× 352+/kloc-0 /× 513+2× 2952 =1.5.