Time and work is one of the important topics from which directly or indirectly many questions are asked in CAT and other management entrance examinations. This chapter is based on the concept of direct and inverse variations. We need to understand relation among time, work done and number of employees working. 

Assuming that all employees work with the same efficiency, we can conclude that work done is directly proportional to number of employees working and number of days to complete the work is inversely proportional to number of employees working. For example if a person does a work in \(x\) days then in 1 day he does only \(\frac{1}{x}\)th of the work and in \(n\) number of days, he will complete \(\frac{n}{x}\) part of the work. Similarly if two men can complete a work working alone in 10 and 20 days respectively, then one day’s work of both the men will be \(\frac{1}{{10}} + \frac{1}{{20}} = \frac{3}{{20}}\). Thus the total work can be completed by both of them in \(\frac{1}{{3/20}} = \frac{{20}}{3}\) days.