In the short run, marginal cost changes due to changes in

Question

Accepted Answer

The correct option is 2:
In the short run, Marginal Cost (MC) is the change in Total Cost (TC) resulting from producing one additional unit of output. The fundamental distinction of the short run in economics is that at least one factor of production (and therefore, some costs) is fixed, while others are variable. Since Total Cost (TC) is the sum of Total Fixed Cost (TFC) and Total Variable Cost (TVC), the change in TC when output increases must come solely from the change in TVC, because TFC remains constant regardless of the output level. Therefore, Marginal Cost (MC) is directly related to the change in Variable Cost, meaning MC = change in TC / change in quantity, which is equivalent to change in TVC / change in quantity. This relationship confirms that MC is determined entirely by the changes in variable input costs in the short run.

The incorrect option is 1:
Fixed cost is the cost associated with fixed factors of production (like rent, machinery depreciation) and does not change with the level of output in the short run. Because fixed costs are constant, they cannot cause a change in the marginal cost (the cost of producing one *more* unit).

The incorrect option is 3:
Total cost is the sum of fixed cost and variable cost (TC = TFC + TVC). While marginal cost is calculated from the change in total cost (ΔTC), the *reason* TC changes in the short run is due to changes in the variable cost, not the total cost itself. Thus, variable cost is the ultimate factor driving the change in MC.

The incorrect option is 4:
Average cost is calculated by dividing total cost by the quantity of output (AC = TC/Q). Average cost is a result of marginal cost and output, not the factor that causes marginal cost to change. While AC curves are influenced by MC, AC itself is a measure of average expenditure, not the source of incremental cost changes.