We need the total count of persons = 10+12+12+15 = 49 persons
We need the count of the target group, female or teaching assistants
= (10+12) professors + 12 male teaching assistants
= 22+12
= 34 persons
Assuming equal probability of choosing anyone from the 30 persons, the
probability of choosing a professor or a male
= 34/49
(For probability calculations, try to keep a fraction for as long as you can, because fractions are exact. Decimal are frequently approximate, for example in this case, 34/49=0.693877551020...... = 0.694 approximately)
