Video Explanation

Text Explanation

Statement #1: given this, we know K = 15 employees are seated, but we have no idea what the size of the larger pool is.  If J is much larger than K, then it becomes unlikely that either Lisa or Phillip is among those seated.  Both would have to be among the seated in order for them to have a chance of sitting next to each other.   Even if J is closer to K, then it becomes more likely that both are among the seated, but we would need to know the number for J to complete the calculation.   This statement, alone and by itself, is insufficient.

Statement #2: Ignore the information in the first statement.  If K = J, then all employees, everyone in the pool of selection, takes a seat.  The problem is—if K = J is a small number, say 4 or 5, then it would be more likely that Lisa and Phillip would wind up next to each other, but if K = J is large, say 200, then its quietly likely that two specific employees wind up nowhere near each other.  The size of K = J would make a big different in the calculation, and without knowing that, we can't calculate.   This statement, alone and by itself, is insufficient.

Combined statements: Now, K = J = 15.  We are seating a group of 15 employees, and we want to know whether two of the people seated, Lisa and Andrew, are next to each other.   This is a calculation we can perform, using counting techniques.   With this combined information, we can give a definitive numerical answer to the prompt question.  Together, the statements are sufficient. 

Statements sufficient together but no individually.   Answer = C

NOTE: I didn't show the calculation for that case, because GMAT DS is all about skipping the calculation if it's not necessary to determine sufficiency.  On the calculation of P, I'll briefly say: denominator = 15!, and numerator is 14 positions for the Lisa-Phillip pair, times two possible orders, times 13! for everyone else.  P = 2/15