Here's why:

• Average Variable Cost (AVC): AVC is calculated as Total Variable Cost (TVC) divided by the quantity of output (Q): AVC = TVC / Q.
• Marginal Cost (MC): MC is the change in TVC resulting from producing one additional unit of output.
• TVC: TVC is the sum of all marginal costs up to that level of output.
• Therefore, AVC = (Sum of MC) / Q, which means AVC is the average of all marginal costs up to that level of output.