The CSUN IEEE chapter is to choose a president treasurer and

The CSUN IEEE chapter is to choose a president, treasurer and secretary, all different, from a group of 10 students. How many different choices of officers are possible if:
a. There are no restrictions
b. A and B will not serve together
c. C and D will serve together or not at all
d. E must be an officer
e. F will serve only if he is a president.

Solution

a.There are no restrictions- 10C3

e. F will serve only if he is a president.-10C1