Feedback Check My Work b. Under variable costing, the cost of goods manufactured includes only variable manufacturing costs. c. What is the reason for the difference in the amount of operating income reported in (a) and (b)? Under the method, the fixed manufacturing cost included in the cost of goods sold is matched with the revenues. Under V, all of the fixed manufacturing cost is deducted in the period in which it is incurred, regardless of the amount of inventory change. Feedback Check My Work b. Under variable costing, the cost of goods manufactured includes only variable manufacturing costs. c. What is the reason for the difference in the amount of operating income reported in (a) and (b)? Under the method, the fixed manufacturing cost included in the cost of goods sold is matched with the revenues. Under V, all of the fixed manufacturing cost is deducted in the period in which it is incurred, regardless of the amount of inventory change