The probability of choosing one of them is 2 out of 75 while the probability of choosing the other one is 1 out of 74. 74 band members, not counting the other person (you or your bother).
Computation: P = 2 / 75 * 1 / 74 = 0.0266... * 0.01351... = 1 / 2,775 You can also multiply 75 with 74 to get a total of 5,550 then divide it by 2 students to be selected to get 2,775. Meaning one out of 2,775 possibilities.
