What is the total number of days that Carpenter Z will take to make one piece each of all the four items together?

If Carpenters X, Y and Z were to make a table together how many days would they take ?

If Carpenter X and Carpenter Y were to make a chair together how many days would they take?

What was the average profit earned by shopkeeper R in the months of October – 2009 and November – 2009 together ?

What is the difference in profit earned by shopkeeper T in January - 2010 from the previous month ?

Which shopkeeper’s profit kept increasing continuously over the given months ?