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?
Pick one.
A) 2
B) 4
C) 6
D) 8
E) 10
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 8.
<result>D</result>
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?