Bunuel wrote:

At a certain university, all employees can be categorized as either professors or administrators, and the average professor earns $18,000 more than the average administrator. How much less does the average administrator earn than the average employee at the university?

(1) The average salary of a professor is $88,000.

(2) There are twice as many administrators as professors.

Analyzing question stem -

Let there be "x" professors & "y" administrators. Also let the average salary of administrator be "a"

So average salary of professor = a+18,000

This implies average salary of ALL the employees will be = {(a+18,000)*x+a*y} / (x+y)____[i.e. total salary of all employees upon total number of employees]

As the question asks us to find out the difference between administrator's average salary and average salary of all employees

= {(a+18,000)*x+a*y}/(x+y) - a = (ax+ay+18000x - ax+ay) / (x+y)

Or, 18000x / (x+y) -----------------(Eq.1)

So we only need relation between number of professors and number of administrators.

Statement 1: Provides no info about number of profs & number of admin. Hence Insufficient

Statement 2: Directly provides the relation between no. of profs. & no. of admin. Hence sufficient. (you can substitute the value in eq.1 to get the exact value but for DS it is not required)

Hence Option

B