How many different ways can 2 students be seated in a row of 7 desks, so that there is always at least one empty desk between the students? Choose one
A) 2  B) 3  C) 30  D) 6  E) 12

Rationale: 15 ways to seat the students : with two empty seats between 1 empty w / one student on the left most 1 empty . . . . right most two students can be interchanged 15 x 2 = 30 c
Answer: C