Total, Marginal, and Average Revenue for a Competitive Firm - Principles of Micro - Mankiw Ch 15

Competitive firms are "price takers" meaning they are too small to have an influence on the market price. Thus, they take the market's price for their good as a given and that price is their marginal revenue per unit, and, if each unit sells for the same price, also their average revenue. The story gets a little more complicated with oligopoly and monopoly but in this video we are just solidifying ideas.