Solution: (1) According to the meaning of the question, a=0.04×5× 1000=200, B = 0.02× 5×1000 =100 ... (4 points).

(2) If the number of students with excellent grades is X, then X40 = 350+300+1001000, then the solution is: x=30,

That is, the number of students with excellent grades is 30 ... (7 points)

(3) According to the meaning of the question, the value of X is 0, 1 2, p (x = 0) = C2 10C240 = 352, p (x =1) = c110c60.

So the distribution list of x is

X 012p3525132952ex = 0× 352+1× 513+2× 2952 = 32, so the mathematical expectation of x is 32 ...