📚 GCSE OCR Economics: Formula Handbook | GCSE OCR 经济：公式汇总手册
Welcome to the GCSE OCR Economics Formula Handbook. This guide brings together all the essential formulas you need across both micro and macro topics – from price elasticity to national income. Use it to reinforce your understanding and quickly revise key quantitative relationships before exams.
欢迎使用 GCSE OCR 经济公式手册。本手册汇总了微观与宏观部分所有重要公式——从价格弹性到国民收入。用它来加深理解，帮助你在考前快速复习关键的数量关系。
1. Price Elasticity of Demand (PED) | 需求价格弹性 (PED)
Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in the good's own price.
需求价格弹性（PED）衡量需求量对商品自身价格变化的反应程度。
PED = %ΔQD / %ΔP
PED = %ΔQD / %ΔP
Percentage change is calculated as: %Δ = (New Value – Original Value) / Original Value × 100.
百分比变动计算公式：%Δ = (新值 – 原值) / 原值 × 100。
Interpretation: if |PED| > 1, demand is price elastic; if |PED| < 1, demand is price inelastic; |PED| 1 gives unit elasticity; PED = 0 is perfectly inelastic; and PED → ∞ is perfectly elastic.
解读：若 |PED| > 1，需求富有弹性；|PED| < 1，需求缺乏弹性；|PED| = 1 为单位弹性；PED = 0 完全无弹性；PED → ∞ 完全弹性。
2. Income Elasticity of Demand (YED) | 需求收入弹性 (YED)
Income elasticity of demand (YED) captures how quantity demanded changes when consumer income changes.
需求收入弹性（YED）反映需求量随消费者收入变动的反应程度。
YED = %ΔQD / %ΔY
YED = %ΔQD / %ΔY
A positive YED indicates a normal good; a negative YED signals an inferior good. If YED > 1, the good is a luxury; if 0 < YED < 1, it is a necessity.
YED 为正表示正常品；负值表示劣等品。若 YED > 1 为奢侈品；0 < YED < 1 则为必需品。
3. Cross Elasticity of Demand (XED) | 需求交叉弹性 (XED)
Cross elasticity of demand (XED) measures the responsiveness of demand for one good (A) to a change in the price of another good (B).
需求交叉弹性（XED）衡量一种商品 (A) 的需求量对另一种商品 (B) 价格变动的反应程度。
XED = %ΔQD of A / %ΔPB
XED = %ΔQD of A / %ΔPB
ds are substitutes; if XED < 0, they are complements; if XED ≈ 0, the goods are unrelated.
若 XED > 0，两者为替代品；XED < 0 则为互补品；XED ≈ 0 表示不相关商品。
4. Price Elasticity of Supply (PES) | 供给价格弹性 (PES)
Price elasticity of supply (PES) indicates how responsive quantity supplied is to a change in the good's own price.
供给价格弹性（PES）显示供给量对商品自身价格变动的反应程度。
PES = %ΔQS / %ΔP
PES = %ΔQS / %ΔP
stic; PES = 1 is unit elastic; PES = 0 perfectly inelastic; and PES → ∞ perfectly elastic.
PES > 1 供给富有弹性；PES < 1 供给缺乏弹性；PES = 1 为单位弹性；PES = 0 完全无弹性；PES → ∞ 完全弹性。
5. Costs of Production | 生产成本
Total cost (TC) is the sum of all fixed and variable costs.
总成本（TC）是所有固定成本与可变成本之和。
TC = FC + VC
TC = FC + VC
Average total cost (ATC or AC) is the cost per unit of output.
平均总成本（ATC 或 AC）是每单位产出的成本。
AC = TC / Q
AC = TC / Q
Average fixed cost (AFC) spreads fixed costs over output.
平均固定成本（AFC）将固定成本分摊到产出上。
AFC = FC / Q
AFC = FC / Q
Average variable cost (AVC) is variable cost per unit.
平均可变成本（AVC）是每单位的可变成本。
AVC = VC / Q
AVC = VC / Q
Marginal cost (MC) is the additional cost of producing one more unit.
边际成本（MC）是额外生产一单位产品所增加的成本。
MC = ΔTC / ΔQ
MC = ΔTC / ΔQ
6. Revenue and Profit | 收益与利润
Total revenue (TR) is the money a firm receives from selling its output.
总收益（TR）是企业销售产品所获得的货币收入。
TR = P × Q
TR = P × Q
Average revenue (AR) is revenue per unit, which equals
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