Price Elasticity of Demand: Calculation & Application | 需求价格弹性：计算与应用

📚 Price Elasticity of Demand: Calculation & Application | 需求价格弹性：计算与应用

Price elasticity of demand (PED) is one of the most important concepts in IGCSE Economics. It measures how much the quantity demanded of a good responds to a change in its price. Understanding PED helps firms, consumers and governments make better pricing and policy decisions.

需求价格弹性（PED）是 IGCSE 经济学中最重要的概念之一。它衡量商品需求量对其价格变动的反应程度。理解 PED 有助于企业、消费者和政府做出更好的定价与政策决策。

1. Definition of Price Elasticity of Demand | 需求价格弹性的定义

Price elasticity of demand is the responsiveness of quantity demanded to a change in price. It compares the percentage change in quantity demanded with the percentage change in price.

需求价格弹性是指需求量对价格变化的反应程度。它将需求量的百分比变化与价格的百分比变化进行比较。

For example, if a product’s price rises by 10% and the quantity demanded falls by 20%, demand is relatively responsive. If the quantity demanded falls by only 2%, demand is relatively unresponsive.

例如，如果某商品价格上涨 10%，而需求量下降 20%，说明需求反应较大；如果需求量仅下降 2%，则说明需求反应较小。

2. The Formula for PED | PED 的计算公式

The basic formula for PED is:

PED 的基本计算公式为：

PED = %ΔQd ÷ %ΔP

Here, %ΔQd is the percentage change in quantity demanded, and %ΔP is the percentage change in price. Because price and quantity demanded usually move in opposite directions, PED is normally negative. In exams, we often take the absolute value and compare it with 1.

其中，%ΔQd 是需求量的百分比变化，%ΔP 是价格的百分比变化。由于价格与需求量通常呈反方向变动，PED 通常为负数。考试中我们常取绝对值，再与 1 比较。

3. Calculating Percentage Changes | 计算百分比变化

To use the formula, you must first calculate the percentage change in quantity and the percentage change in price. For each change, divide the amount of change by the original value, then multiply by 100.

要使用公式，必须先计算需求量的百分比变化和价格的百分比变化。每次变化都用变化量除以原来的数值，再乘以 100。

%ΔQ = (Q₂ − Q₁) ÷ Q₁ × 100

%ΔP = (P₂ − P₁) ÷ P₁ × 100

In these formulas, Q₁ and P₁ are the original values, while Q₂ and P₂ are the new values after the change.

在这些公式中，Q₁ 和 P₁ 是原来的数值，Q₂ 和 P₂ 是变化后的新数值。

4. Worked Example: From $6 to $9 | 计算示例：从 6 美元到 9 美元

Suppose the price of a bus ticket rises from $6 to $9. As a result, the number of journeys demanded falls from 120 to 90 per day.

假设公交车票价从 6 美元上涨到 9 美元。结果，每天需求量的出行次数从 120 次下降到 90 次。

First, calculate the percentage change in price:

首先计算价格的百分比变化：

(9 − 6) ÷ 6 × 100 = 50%

Second, calculate the percentage change in quantity demanded:

其次计算需求量的百分比变化：

(90 − 120) ÷ 120 × 100 = −25%

Therefore, PED = −25% ÷ 50% = −0.5. Taking the absolute value gives 0.5. Because 0.5 is less than 1, demand is price inelastic.

因此，PED = −25% ÷ 50% = −0.5。取绝对值得到 0.5。因为 0.5 小于

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