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 correct choice from the following.
A) 10 days
B) 230 days
C) 50 days
D) 40 days
E) 20 days
B   30 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 230 days 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   230 days’s one day's work=1/48   (A+230 days)'s one day's work=1/80+1/48=8/240=1/30   Hence, both will finish the work in 30 days.
<result>B</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?