If 8 workers can build 8 cars in 8 days, then how many days would it take 6 workers to build 6 cars?  Pick: A) 2 B) 4 C) 6 D) 8 E) 12

Rationale: "8 workers can build 1 car per day on average . 1 worker can build 1 / 8 of a car per day . 6 workers can build 6 / 8 car per day . the time required to build 6 cars is 6 / ( 6 / 8 ) = 8 days the answer is d ."
Answer: D