1. If 1/n of a work is done by A in one day, then A will take n days to complete the full work.

2. If A can do a piece do a piece of work in X days and B can do the same work in Y days, then both of them working together will do the same work in XY/(X+Y) days

3. If A, B and C, while working alone, can complete a work in X, Y and Z days respectively, then they will together complete the work in XYZ/(XY+YZ+ZX) days

4. If A does 1/nth of a work in m hours, then to complete the full work A will take nxm hours.

5. If A and B can together finish a piece of work in X days, B and C in Y days and C and A in Z days, then a) A, B and C working together will finish the job in (2XYZ/XY+YZ+ZX) days. b) A alone will finish the job in (2XYZ/XY+YZ- ZX) days. c) B alone will finish the job in (2XYZ/ZX+XY- YZ) days. d) C alone will finish the job in (2XYZ/ZX+YZ- XY) days

6. If A can finish a work in X days and B is k times efficient than A, then the time taken by both A and B working together to complete the work is X/(1+k).

7. If A and B working together can finish a work in X days and B is k times efficient than A, then the time taken by A working alone to complete the work is (k+1)X and B working alone to complete the work is (k+1/k)X.