A can do a piece of work in 80 days. He works at it for 10 days & then B alone finishes the remaining work in 42 days. In how much time will A and B, working together, finish the work? Choose the most appropriate option
A) 20 days  B) 10 days  C) 30 days  D) 60 days  E) 50 days
Work done by A in 10 days=10/80=1/8   Remaining work=(1-(1/8))=7/8   Now, work will be done by B in 42 days.   Whole work will be done by B in   (42*8/7)= 
<gadget id="calculator">  (42*8/7)</gadget>
<output>48</output>
48 days   Therefore, A's one day's work=1/80   B’s one day's work=1/48   (A+B)'s one day's work=1/80+1/48=8/240=1/30   Hence, both will finish the work in 30 days.   Answer : 30 days.
<result>C</result>
A can do a piece of work in 80 days. He works at it for 10 days & then B alone finishes the remaining work in 42 days. In how much time will A and B, working together, finish the work?