# Using aggregate marginal revenue as a way to estimate demand

We also know that for a competitive market, the supply curve is the sum of the marginal cost curves.

Can one make an extension of this idea to having the demand curve being equal to the sum of marginal revenue curves with its slope coefficient doubled?

• Are you assuming linear demand or not? – Giskard Apr 25 '18 at 9:42
• P.s.: This can be seen as nitpicking but the supply curve is not the sum marginal cost curves. Supply is a function of price and marginal cost is a function of quantity. – Giskard Apr 25 '18 at 9:43
• @denesp I guess I am assuming linear demand now that you mention it. Can you give me a source for the claim "Supply is a function of price and marginal cost is a function of quantity." as I'm currently of the impression that it doesn't matter given the basic supply and demand framework. – EconJohn Apr 25 '18 at 16:14
• Will Wikipedia do? "Supply is often plotted graphically with the quantity provided (the dependent variable) plotted horizontally and the price (the independent variable) plotted vertically." (Emphasis by me.) – Giskard Apr 25 '18 at 16:55