1. A and B can together do a piece of work in 15 days. B alone can do it in 20 days. In how many days can A alone do it ?

2. A is twice as good a workman as B and together they finish a piece of work in 14 days. A alone can finish the work in:

3. A can do a piece of work in 80 days. He works at it for 10 days and then B alone finishes the work in 42 days. The two together could complete the work in: