Final answer:
Angela's constant expenditure on iPhone apps despite the price decline implies a perfectly inelastic demand. The decrease in price does not necessarily mean that the supply curve has decreased; it may indicate increased supply due to factors like new technology or economies of scale.
Step-by-step explanation:
Angela finds that her total expenditure on iPhone apps remains the same after the price of iPhone apps declines, assuming other factors remain constant (ceteris paribus). This phenomenon suggests that Angela's demand for apps is perfectly inelastic, which means she spends a fixed amount on apps irrespective of the price changes.
In other words, the quantity of the apps she downloads has increased proportionally to offset the price decrease, keeping her total spending unchanged. However, this user behavior does not directly imply that the supply curve for iPhone apps has decreased—it could be that the market supply is responding to an overall increase in demand. If the supply curve did decrease with the price, then we would typically see an increase in the price of apps due to scarcity, which contradicts the observed price decline. It is more plausible that the supply curve has shifted to the right, reflecting an increase in supply, which could be due to reasons such as new technology or economies of scale, according to the principles of a constant-cost industry.