Market Demand Curve We already talked about an individual demand curve (remember the cupcake example from earlier); sometimes we need to know the quantities demanded by everyone who is interested in buying a product. This kind of demand curve is called the Demand and Marginal Utility Earlier in the course, we said that utility is the amount of one gets from using a product. So, marginal utility is the extra usefulness/satisfaction one gets from getting or using one more unit of a product