A company has a hierarchical system where for every 10 workers, there is one team lead, and for every 3 teams leads, there is one supervisor. If the company has 13 supervisors, how many workers does it have?	Choose one:
A) 140	B) 321	C) 390	D) 500	E) 130

Rationale: some students may initially answer 130 to this question , especially if answering similar problems . however , that would be incorrect , as this is not a straight - forward ratio of 1 : 3 : 10 . the ratio of supervisors to team leads is 1 : 3 , and the ratio of team leads to workers is 1 : 10 . therefore , the ratio of supervisors to workers is 1 : 30 . therefore , 13 * 30 = 390 answer : c )
Answer: C