Each student has four courses to choose from, and three students are 4 3 = 64.

There are two of the four courses, C (4,2), and each student has only two choices, and three students are 2 3.

Probability: c (4 4,2) * 2 3/4 3 = 3/4.

2)

0 Probability of candidates: 3 3/4 3 = 27/64

1 candidate probability: c (3, 1) * 3 2/4 3 = 27/64.

2 Candidate probability: c (3 3,2) * 3/4 3 = 9/64.

3 Candidate probability: c (3 3,3) * 3/43 =1/64.

Mathematical expectation: 0 * 27/64+1* 27/64+2 * 9/64+3 *1/64 = 3/4.