Suppose there are 20 consumers for a good and they have identical demand functions:

d(p) = 10 – 3p for any price less than or equal to 10/3 and d₁(p) = 0 at any price greater than 10/3.

What is the market demand function?

d(p) = 10 – 3p if Price ≤ 10/3

d₁(p) = 0 if Price > 10/3

Market Demand is total demand of all consumers

For Price ≤ 10/3

Market Demand = 20 (10 – 3p)

= 200 – 60p

For Price > 10/3

Market Demand = 20 (0)

= 0

Therefore, market demand function is

200 – 60p if Price ≤ 10/3

0 if Price > 10/3