Final answer:
The price of pens decreasing and the price change of apples affect the Change in Quantity as both reflect a move along the demand curve. Meanwhile, Annie buying more pens due to a raise and Billy buying more apples due to the price of oranges rising signify a Change in Demand, as these are shifts in the demand curve due to factors other than the price of the good itself.
Step-by-step explanation:
In economics, understanding how various factors affect consumer behavior is crucial. The statements provided can be categorized into two groups based on how they are influenced by different market changes. There's Change in Quantity and Change in Demand. The Change in Quantity denotes a change in the quantity demanded due to a price change, while Change in Demand implies an actual shift in the demand curve due to other factors apart from the price.
- Change in Quantity:
- The price of pens decreases.
- If the price of apples changes, Billy will change how many apples he buys.
- Change in Demand:
- Since Annie got a raise, she buys more pens.
- The price of oranges rises, the price of apples does not change. Therefore, Billy buys more apples.
The first statement suggests a move along the demand curve due to a price change, which is a Change in Quantity. The second statement also represents a Change in Quantity demanded because it's reliant on the price of apples. The third statement, suggesting that Annie's income increased and therefore she buys more pens, indicates a Change in Demand since her income level is affecting her purchasing decision. Similarly, the fourth statement represents a Change in Demand because the substitution effect between apples and oranges, which are substitute goods, is at play rather than a direct price change of apples themselves.