20 beavers, working together in a constant pace, can build a dam in 18 hours. How many hours will it take 12 beavers that work at the same pace, to build the same dam?
Choices.
A) 22 . B) 24 . C) 30 . D) 36 E) 38 .

Rationale: total work = 20 * 18 = 360 beaver hours 12 beaver * x = 360 beaver hours x = 360 / 12 = 30 answer : c
Answer: C