Suppose there is a unit mass of consumers (this language means that there are infinitely many consumers who are all minuscule and together add to a 'mass; of 1; each consumer is treated like a realization of a continuous random variable drawn from a continuous distri- bution, in effect.) Each consumer demands either zero or one unit of the good, depending if the market price p exceeds or is below the consumer's valuation v.

Suppose that consumers' valuations are distributed uniformly on the interval [0, 3]. Question: What is aggregate demand?

Step 1 is to consider an individual consumer. Given a valuation of v, what is the demand? Step 2 is to 'sum' all demands, or, which is the same thing here, to figure out how many

consumers there are that buy 1 unit at a given price.