5. Aggregate Demand

What survives when individual demands are added up — the properties of aggregate demand and the representative consumer.

• Aggregating Demand — This scene adds three consumers into one demand. Stack their curves together and the market curve appears. Some properties survive the adding-up. If everyone spends their whole budget, so does the market. Double every price and income together, and demand stays put. Move each person's curve and check for yourself. For example, three 🧑 classmates buy 🍎 apples. The first buys 2, the second 3, the third 5. Together the class buys 10 apples. If prices and 💰 allowances all double, the count stays the same.
• The Representative Consumer — This scene asks whether many people can act as one. Shuffle money between two people with identical tastes. However the money is split, aggregate demand never moves. What one person loses, the other gains exactly. Only the total amount of money matters. Then a representative consumer exists. The whole market computes like one imaginary person. For example, twin brothers split a 💰 allowance of 12,000 won. The older may take 8,000 and the younger 4,000. Swap the split, and the 🍎 apples they buy stay the same. Only the total matters, not who holds what.