A can do a piece of work in 80 days. He works at it for 10 days B alone finishes the remaining work in 42 days. In how much time will A and B working together, finish the work?  Pick one:
A) 25	B) 30	C) 20	D) 32	E) None of them
Work done by A in 10 days =(1/80*10)=1/8   Remaining work = (1- 1/8) =7/ 8   Now,7/ 8 work is done by B in 42 days.   Whole work will be done by B in (42 x 8/7) = 48 days.   A’s 1 day's work = 1/80 and B's 1 day's work = 1/48   (A+B)'s 1 day's work = (1/80+1/48)=8/240=1/30   Hence, both will finish the work in 30 days.   Answer is 30.
<result>B</result>
A can do a piece of work in 80 days. He works at it for 10 days B alone finishes the remaining work in 42 days. In how much time will A and B working together, finish the work?