For a perfect competitor, the price will always be equal to the marginal revenue, while in case of monopoly the price will always be greater than the marginal cost. When a monopolist is making a normal profit, it doesn’t necessarily mean that it has to be at the lowest point of the average cost curve. And in this example that is 20. So marginal revenue and price are the same for our perfect competitor. So that means that this is what their demand curve looks like. This is a perfectly elastic demand curve, which shows that there's only one price, and in our example it was $20. It's marginal revenue, it's their demand curve, it's also price.