Working individually, Allison can sew dresses for 9 hours and Al can sew dresses in 12 hours. If Allison and Al work together but independently at the task for 3 hours, at which point Al leaves, how many remaining hours will it take Allison to complete the task alone?
Select.
A) 45 / 12  B) 23 / 12  C) 40 / 33  D) 34 / 12  E) 43 / 5

Rationale: in first 3 hrs al will finish 3 / 12 = 1 / 4 of work and allison will finish 3 / 9 = 1 / 3 work so total 1 / 4 + 1 / 3 = 7 / 12 work is finished and 1 - 7 / 12 = 5 / 12 work remaining . now allison will take ( 5 / 12 ) * 9 = 45 / 12 hrs to finish it . so answer is a .
Answer: A