(1)3 students and 2 people pass: the probability of each person passing is:

Answer: 0.5×0.5 (twice)

B: (three shots) b 1, no, 0.5×0.5×0.5+b2 No, 0.5×0.5×0.5.

C: (4 beats) c 1, no, no, 0.5×0.5×0.5 ×0.5.

C2 No, medium, no, medium 0.5×0.5×0.5.

C3 No, no, medium, medium 0.5×0.5×0.5.

Everyone goes through customs p = a+b+c =1116.

Everyone can't pass P' = 1-P = 5/ 16.

So: just two people go through customs for c (3,2) × p× p× (1-p).

(2) At least one person has passed the customs: one person has not passed the customs, that is, p'×P'×P'

So: p= 1-p'×P'×P'