Dan can do a job alone in 15 hours. Annie, working alone, can do the same job in just 10 hours. If Dan works alone for 3 hours and then stops, how many hours will it take Annie, working alone, to complete the job?  Select
A) 2	B) 4	C) 6	D) 8	E) 10

Rationale: "dan can complete 1 / 15 of the job per hour . in 3 hours , dan completes 3 ( 1 / 15 ) = 1 / 5 of the job . annie can complete 1 / 10 of the job per hour . to complete the job , annie will take 4 / 5 / 1 / 10 = 8 hours . the answer is d ."
Answer: D