total COST吾=sum of marginal?

由你的問題反映，你的經濟是英文任教，故此你的問題，我將以英文解釋。

Marginal cost is calculated by the difference between the total cost of a particular output(n) and the total cost of the previous outpust(n-1)

Let me get an example :

Output(unit) Total Cost($) Marginal cost($)
1 aaaaaaaaaaaaaaa5 aaaaaaaaaaaa /
2 aaaaaaaaaaaaaaa11 aaaaaaaaaaa 6
3 aaaaaaaaaaaaaaa18 aaaaaaaaaaaa7
4 aaaaaaaaaaaaaaa26 aaaaaaaaaaaa8

In different output, there can have different cost as there is fixed factors and varible factors.

Sum of Marginal cost = 6+7+8 = 21
Sum of Total Cost = 5+11+18+26 = 60

Sum of marginal Cost is not equal to sum of total cost.

希望能解答你的問題。

Sum of Marginal cost = 6+7+8 = 21
Total Cost = 26 (i.e. cost of first item + sum of marginal cost = 5 + 21)

Sum of marginal Cost is not equal to sum of total cost.