**Relation between Total, Average and Marginal Product**

**Returns to a factor :**In a short period when additional units of variablefactors are employed with fixed factors, then returns to a factor operates. Returns to a factor shows the changes in total products, of a good when

**Law of variable proportion :**The law states that as we increase thequantity of only variable one input, keeping other inputs fixed, the total product increases at increasing rate in the beginning, then increases at decreasing rate and finally TP falls. According to this law, change in TP and MP are classify into three shares.

**Phase I : TP Increases at increasing rate :**In the initial phase asmore and more units of variable factor are employed with fixed factor total physical production increases at increasing rate, MP increases.

**Phase II : TP increases at decreasing rate :**As more and moreunits of variable factors are employed with fixed factors then total product increases at diminishing rate, MP decreases but is positive. At the end of this phase TP maximum and MP becomes zero.

**Phase III : TP falls :**As more and more units of variable factorsare employed with given fixed factors, total production starts decreasing and marginal product becomes negative.

**Economic Cost :**It is the sum of direct (explicit cost) and indirect cost(explicit cost), including Normal profit.

**Economic cost :**Explicit cost + implicit cost + Normal Profit.