Horizontal Summation of Individual Demand Curves

Steps:

• Identify individual demand curves showing quantity demanded at different prices for each consumer.
• To find market demand, sum quantities demanded by all consumers at each price level.
• This summation occurs along the horizontal axis (quantity), keeping price (vertical axis) fixed.
• Plot the summed quantities against the same prices to get the market demand curve.

Why B is correct:

• Market demand is derived by horizontally summing individual demands, as defined in microeconomics: at each price, total quantity is the sum of individual quantities (Q_market = Σ Q_i).

Why the others are wrong:

• A: Vertical summation applies to supply curves, not demand.
• C: Only horizontal works for demand; vertical does not aggregate quantities properly.
• D: Vertical summation would incorrectly add prices, violating demand curve construction.

Final answer: B