A alone can complete a piece of work in 18 days and B alone in 15 days, B alone worked at it for 10 days and then left the work. In how many more days, will A alone complete the remaining work ?

$$\eqalign{ & {\text{B's}}\,{\text{10}}\,{\text{day's}}\,{\text{work}} \cr & = \left( {\frac{1}{{15}} \times 10} \right) = \frac{2}{3} \cr & {\text{Remaining}}\,{\text{work}} \cr & = \left( {1 - \frac{2}{3}} \right) = \frac{1}{3} \cr & {\text{Now}},\frac{1}{{18}}{\text{work}}\,{\text{is}}\,{\text{done}}\,{\text{by}}\,{\text{A}}\,{\text{in}}\,{\text{1}}\,{\text{day}} \cr & \therefore \frac{1}{3}\,{\text{work}}\,{\text{is}}\,{\text{done}}\,{\text{by}}\,{\text{A}}\,{\text{in}} \cr & \left( {18 \times \frac{1}{3}} \right) = 6\,{\text{days}} \cr} $$