Worker A takes 10 hours to do a job. Worker B takes 15 hours to do the same job. How long it take both A & B, working together but independently, to do the same job?	Pick:  A) 40 days  B) 40/9 days  C) 39/9 days  D) 6 days  E) 60/9 days
A's one hour work = 1/10.   B's one hour work = 1/15.   (A+B)'s one hour work = 1/10+1/15 = 5/30 = 1/6.   Both A &amp; B can finish the work in 6 days   6 days
<result>D</result>
Worker A takes 10 hours to do a job. Worker B takes 15 hours to do the same job. How long it take both A & B, working together but independently, to do the same job?