Question 321004
4 P-professors, 
7 A-associate professors
6 S-assistant professors
9 I-instructors
26 total
P(P)={{{4/26}}}
P(I)={{{9/26}}}
P(P or I)=P(P)+P(I)
P(P or I)={{{(4+9)/26=13/26=1/2}}}