Worker A takes 12 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?	Select.
A) 40 days	B) 40/9 days	C) 39/9 days	D) 30/9 days	E) 20/3 days
A's one hour work = 1/12.   B's one hour work = 1/15.   (A+B)'s one hour work = 1/12+1/15 = 9/60 = 3/20.   Both A &amp; B can finish the work in 20/3 days   20/3 days
<result>E</result>
Worker A takes 12 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?