Alright, now let's discuss revenue in perfect competition and define average revenue and marginal revenue. We've talked about revenue before, and not much is changing here. Revenue is the money coming into the firm. We're going to say that our total revenue is going to be equal to the price times the quantity, right? Whatever price we sell at times the quantity we sell, that's all the money that we're going to bring in. So when we talk about revenues, these are the benefits to the firm. When we think about benefits, remember we're talking about marginal benefits and marginal costs? These would be the benefits to the firm. A marginal benefit to the firm would be how much more revenue we can get when we sell 1 more unit.
Let's dive into average revenue and marginal revenue, important concepts throughout all of these chapters, and see how it relates in perfect competition. We always label average revenue as AR for average revenue and marginal revenue as MR. Let's start with average revenue. Average revenue means to divide by Q, the quantity. We're going to take our total revenue and divide it by quantity. Total revenue, which is price times quantity, divided by quantity results in the quantities canceling out, leaving us with P. Average revenue equals P. This formula shows that average revenue always equals the price, which is also our demand curve. This is true for all market structures, not just perfect competition, so every market structure's average revenue equals price and is also the demand curve.
Now let's talk about marginal revenue. Marginal revenue equals the change in total revenue over the change in quantity. Marginal refers to what happens when we add one more unit. If we sell one more unit, how much more revenue are we going to get? This formula, the change in total revenue over the change in quantity, usually considers a single additional unit. In perfect competition, the price is fixed for the firm; the market sets the price, and the firm has to sell all its products at that price. The firm can sell as much as it wants and will always sell at this price. If the firm decides to increase its quantity by 1, it will sell that unit at the market price, which doesn't change because the firm increased its production. They sold one more unit for P, and the change in total revenue was P. Therefore, the marginal revenue is going to be equal to the price as well in perfect competition. If you want to sell 1 more unit, you'll bring in 1 more price worth of revenue. This conclusion, that the marginal revenue equals price and the average revenue equals the marginal revenue equals price, is true only for perfect competition.
This is a special case in perfect competition and leads to special outcomes in this market. In the next video, we'll discuss how this marginal revenue stays constant at the price with a numerical example to illustrate what this means in action. Let's do that now.