Marginal cost

The marginal cost is also a per unit cost of production . It is the addition mode to the total cost by producing one more unit of output. Symbolically Mcn =Tcn-Tcn-1 that is the marginal cost nth unit of output is the total cost of producing n unit  minus the total cost of producing     n -1 unit of outputs

For example suppose in production plant total cost of producing 5 chair is Rs 10000 while that for 4 chairs is Rs 8000.
Marginal cost of producing the 4th chair therefore work out as under.

MC5=TC5-TC4 = 10000-8000=2000

Marginal cost is the cost of producing an extra unit of output . It can also be defined as the change in total cost associated with a one unit change in output. It is also known as" extra unit cost "or increment cost. It can also be calculated by dividing  the change in total cost by one unit change in output
Mc = ∆TC/∆1Q
Where ∆ denotes change in output assume to change by 1 unit.