Demand and Supply : Elasticity 需求及供應：彈性

Elasticity of Demand 需求彈性 Elasticity of demand 需求彈性 percentage change in quantity demanded 需求數量的轉變百分比 = percentage change in price 價格的的轉變百分比

Example 例子 : As the price of apples rises from $3.8 to $4.2, the quantity demanded falls from 200 to 120. Calculate the elasticity of demand for apple. 當蘋果的價格由$3.8增加至$4.2，需求數量由200下降至120。計算蘋果的需求彈性。

Elasticity of demand 需求彈性 Qd : 200  120 P : $3.8  $4.2 Elasticity of demand 需求彈性 percentage change in quantity demanded 需求數量的轉變百分比 = percentage change in price 價格的的轉變百分比

percentage change in price Elasticity of demand 需求彈性 Qd : 200  120 P : $3.8  $4.2 percentage change in price 價格的的轉變百分比 = 200 - 120 200 + 120

Elasticity of demand 需求彈性 Qd : 200  120 P : $3.8  $4.2 200 - 120 200 + 120 = Elasticity of demand 需求彈性 Qd : 200  120 P : $3.8  $4.2 80 = 320 $4.2 - $3.8 0.4 $4.2 + $3.8 8

Elasticity of demand 需求彈性 Qd : 200  120 P : $3.8  $4.2 80 320 0.4 8 = Elasticity of demand 需求彈性 Qd : 200  120 P : $3.8  $4.2

Elasticity of demand 需求彈性 Qd : 200  120 P : $3.8  $4.2 = 80 320 0.4 8 80 320 0.4 8 = 5 = X

Example 例子 : As the price of a mini hi-fi system falls from $2500 to $2000, the quantity demanded rises from 350 to 550. Calculate the elasticity of demand for apple. 當一套微型音響組合的價格由$2500下降至$2000，需求數量由350增加至550。計算微型音響組合的需求彈性。

Elasticity of demand 需求彈性 Qd : 350  550 P : $2500  $2000 Elasticity of demand 需求彈性 percentage change in quantity demanded 需求數量的轉變百分比 = percentage change in price 價格的的轉變百分比

percentage change in price Elasticity of demand 需求彈性 Qd : 350  550 P : $2500  $2000 percentage change in price 價格的的轉變百分比 = 550 - 350 550 + 350

Elasticity of demand 需求彈性 Qd : 350  550 P : $2500  $2000 550 - 350 550 + 350 = Elasticity of demand 需求彈性 Qd : 350  550 P : $2500  $2000 200 = 900 $2500 - $2000 500 $2500 + $2000 4500

Elasticity of demand 需求彈性 Qd : 350  550 P : $2500  $2000 900 500 4500 =

Elasticity of demand 需求彈性 Qd : 350  550 P : $2500  $2000 900 500 4500 = 200 900 500 4500 = 2 = X

Types of Elasticity of Demand 需求彈性的種類 Unitary Elastic 單一彈性 Relatively Elastic 相對具彈性 Relatively Inelastic 相對欠彈性 Perfectly Elastic 絕對具彈性 Perfectly Inelastic 絕對欠彈性

Unitary Elastic 單一彈性 Elasticity of demand 需求彈性 = 1 =1 percentage change in quantity demanded 需求數量的轉變百分比 percentage change in price 價格的的轉變百分比 =1

Unitary Elastic 單一彈性 Elasticity of demand 需求彈性 = 1 percentage change in price 價格的轉變百分比 percentage change in quantity demanded 需求數量的轉變百分比 =

Unitary Elastic 單一彈性 Elasticity of demand 需求彈性 = 1 P Q D

Relatively Elastic 相對具彈性 Elasticity of demand 需求彈性 > 1 percentage change in quantity demanded 需求數量的轉變百分比 percentage change in price 價格的的轉變百分比 >1

Relatively Elastic 相對具彈性 Elasticity of demand 需求彈性 > 1 percentage change in price 價格的轉變百分比 percentage change in quantity demanded 需求數量的轉變百分比 >

Relatively Elastic 相對具彈性 Elasticity of demand 需求彈性 > 1 P Q D

Relatively Inelastic 相對欠彈性 Elasticity of demand 需求彈性 < 1 percentage change in quantity demanded 需求數量的轉變百分比 percentage change in price 價格的的轉變百分比 <1

Relatively Inelastic 相對欠彈性 Elasticity of demand 需求彈性 < 1 percentage change in price 價格的轉變百分比 percentage change in quantity demanded 需求數量的轉變百分比 <

Relatively Inelastic 相對欠彈性 Elasticity of demand 需求彈性 < 1 P Q D

Perfectly Elastic 絕對具彈性 Elasticity of demand 需求彈性 =  percentage change in quantity demanded 需求數量的轉變百分比 percentage change in price 價格的的轉變百分比 =

percentage change in quantity demanded 需求數量的轉變百分比 Perfectly Elastic 絕對具彈性 Elasticity of demand 需求彈性 =  percentage change in quantity demanded 需求數量的轉變百分比 =

Perfectly Elastic 絕對具彈性 Elasticity of demand 需求彈性 =  P Q D

Perfectly Inelastic 絕對欠彈性 Elasticity of demand 需求彈性 = 0 percentage change in quantity demanded 需求數量的轉變百分比 percentage change in price 價格的的轉變百分比 =0

percentage change in quantity demanded 需求數量的轉變百分比 Perfectly Inelastic 絕對欠彈性 Elasticity of demand 需求彈性 = 0 percentage change in quantity demanded 需求數量的轉變百分比 =0

Perfectly Inelastic 絕對欠彈性 Elasticity of demand 需求彈性 = 0 P Q D

If the demand curve is a straight line, the elasticity of demand at various points on the demand curve will have a special pattern. 如果需求曲線是一條直線，在需求曲線上各點的需求彈生，會一個特別的模式。

Ed =  P Q Ed > 1 D Ed = 1 Ed < 1 Ed = 0 Mid-point

Factors Affecting the Elasticity of Demand 影響需求彈性的因素 Number of Substitutes 代替品的數目 Degree of Necessity 必需的程度 Habit of Consumers 消費者的習慣 Time for Adjusting Consumption 調整消費的時間

Elasticity of Demand and Tax Burden 需求彈性和稅額負擔 Elasticity of demand can affect the amount of tax shared by consumers and producers. 需求彈性可以影響由消費者負擔的稅額和生產者負擔的稅額。

unit tax 單位稅 S1 S0 P1 Po D Q1 Qo total tax paid by consumers 消費者支付的總稅額 S1 D S0 unit tax 單位稅 Q1 P1 Po Qo total tax paid by consumers 消費者支付的總稅額 total tax paid by producers 生產者支付的總稅額

If demand is inelastic, equilibrium price increases greatly If demand is inelastic, equilibrium price increases greatly. Consumers share a greater tax burden. Producers share a smaller tax burden. 如果需求欠彈性，均衡價格大幅增加，消費者要負擔較大量稅額，生產者負擔較少量稅額。

unit tax 單位稅 S1 S0 P1 Po D Q1 Qo total tax paid by consumers 消費者支付的總稅額 S1 D S0 unit tax 單位稅 Q1 P1 Po Qo total tax paid by consumers 消費者支付的總稅額 total tax paid by producers 生產者支付的總稅額

If demand is elastic, equilibrium price increases slightly If demand is elastic, equilibrium price increases slightly. Consumers share a smaller tax burden. Producers share a greater tax burden. 如果需求具彈性，均衡價格輕微增加，消費者負擔較少量稅額，生產者要負擔較大量稅額。

Elasticity of Demand and Total Revenue 需求彈性和總收益 Total revenue means the amount of money obtained by producers. 總收益是指生產者獲得的總金額。

It is the same as the total expenditure paid by consumers or the total market value of the goods transacted. 這相等於消費者支付的總支出 或 產品交易的總市場價值。

Total Revenue 總收益 x = Price 價格 Quantity 數量 D S P Q total revenue總收益

If price and quantity change, total revenue will also change. 如果價格和數量轉變，總收益亦會轉變。

original total revenue 原本的總收益 new total revenue 新的總收益 P Q S original total revenue 原本的總收益 new total revenue 新的總收益

original total revenue 原本的總收益 S new total revenue 新的總收益 P Q A B C OABC

Price Quantity Total Revenue 價格 數量 總收益       Uncertain 不確定 ?   Uncertain 不確定 ?  

For the uncertain cases, the elasticity of demand determines the change in total revenue. 對於不確定的個案，需求彈性決定了總 收益的轉變。

Relatively Elastic Demand 相對具彈性的需求 For the case with : Relatively Elastic Demand 相對具彈性的需求 Price increases, quantity decreases. 價格增加，數量減少。

original total revenue 原本的總收益 P Q D original total revenue 原本的總收益

P Q D new total revenue 新的總收益

original total revenue 原本的總收益 D P Q D

P Q D

P Q D decrease in revenue 減少的收益 increase in revenue 新增的收益

If demand is relatively elastic, when price increases and quantity decreases, decreases in revenue is greater than increase in revenue. Total revenue decreases. 如果需求是相對具彈性， 當價格增加而數量減少， 減少的收益會大於新增的收益， 總收益會減少。

Relatively Inelastic Demand 相對欠彈性的需求 For the case with : Relatively Inelastic Demand 相對欠彈性的需求 Price increases, quantity decreases. 價格增加，數量減少。

original total revenue 原本的總收益 P Q D original total revenue 原本的總收益

P Q D new total revenue 新的總收益

original total revenue 原本的總收益 D P Q D

P Q D

P Q D decrease in revenue 減少的收益 increase in revenue 新增的收益

If demand is relatively inelastic, when price increases and quantity decreases, decreases in revenue is smaller than increase in revenue. Total revenue increases. 如果需求是相對欠彈性， 當價格增加而數量減少， 減少的收益會少於新增的收益， 總收益會增加。

Relatively Elastic Demand 相對具彈性的需求 For the case with : Relatively Elastic Demand 相對具彈性的需求 Price decreases, quantity increases. 價格減少，數量增加。

original total revenue 原本的總收益 P Q D original total revenue 原本的總收益

P Q D new total revenue 新的總收益

original total revenue 原本的總收益 D P Q D

P Q D decrease in revenue 減少的收益 increase in revenue 新增的收益

If demand is relatively elastic, when price decreases and quantity increases, decreases in revenue is smaller than increase in revenue. Total revenue increases. 如果需求是相對具彈性， 當價格增加而數量減少， 減少的收益會少於新增的收益， 總收益會增加。

Relatively Inelastic Demand 相對欠彈性的需求 For the case with : Relatively Inelastic Demand 相對欠彈性的需求 Price decreases, quantity increases. 價格減少，數量增加。

original total revenue 原本的總收益 P Q D original total revenue 原本的總收益

P Q D new total revenue 新的總收益

P Q D decrease in revenue 減少的收益 increase in revenue 新增的收益

If demand is relatively inelastic, when price decreases and quantity increases, decreases in revenue is greater than increase in revenue. Total revenue increases. 如果需求是相對欠彈性， 當價格減少而數量增加， 減少的收益會大於新增的收益， 總收益會減少。

Price Quantity Total Revenue 價格 數量 總收益 Elastic 具彈性       Inelastic 欠彈性      

Price Quantity Total Revenue 價格 數量 總收益   Elastic 具彈性 Inelastic 欠彈性

Price Quantity Total Revenue 價格 數量 總收益   Elastic 具彈性 Inelastic 欠彈性

Elasticity of Supply 供應彈性 Elasticity of supply 供應彈性 percentage change in quantity supplied 供應數量的轉變百分比 = percentage change in price 價格的的轉變百分比

Types of Elasticity of Supply 供應彈性的種類 Unitary Elastic 單一彈性 Relatively Elastic 相對具彈性 Relatively Inelastic 相對欠彈性 Perfectly Elastic 絕對具彈性 Perfectly Inelastic 絕對欠彈性

Unitary Elastic 單一彈性 Elasticity of supply 供應彈性 = 1 P Q S

Unitary Elastic 單一彈性 Elasticity of supply 供應彈性 = 1 P Q S

Relatively Elastic 相對具彈性 Elasticity of supply 供應彈性 > 1 P Q S

Relatively Elastic 相對具彈性 Elasticity of supply 供應彈性 > 1 P Q S

Relatively Inelastic 相對欠彈性 Elasticity of supply 供應彈性 < 1 P Q S

Relatively Inelastic 相對欠彈性 Elasticity of supply 供應彈性 < 1 P Q S

Perfectly Elastic 絕對具彈性 Elasticity of supply 供應彈性 =  P Q S

Perfectly Inelastic 絕對欠彈性 Elasticity of supply 供應彈性 = 0 P Q S

Factors Affecting the Elasticity of Supply 影響供應彈性的因素 Flexibility of Production 生產的靈活性 Ease of Entry into Market 容易進入市場的程度 Amount of Stocks 存貨的數量 Time for Adjusting Consumption 調整消費的時間

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