计算需求价格弹性 运用中点公式计算需求价格弹性 Computing the Price Elasticity computing the Price Elasticity of Demand Using the Midpoint of demand Formula Percentage change in quatity demanded ◆如果你试图计算需求曲线上两点之 格弹性,你马上就会注意到一个恼 如果冰演淋蛋卷的价格从20美元上升到220美元,你所购买 从A点到B点的弹性,与从B点到A点 量从10个下障到8个,那么你的需求弹性可以计算如下: 不同的。 ao plei: the he prict of a bie e reases from S2. 00 to t you buy falls from 10 to 8 cones then your If you try calculate the price elasticity of elasticity of demand would he caleulated as demand between two points on a demand curve, you will quickly notice an annoying -20 percent problem: The elasticity from point A to point B seems different from the elasticity from point B 2.20-20×10010 percent 运用中点公式计算需求价格弹性 运用中点公式计算需求价格弹性 Computing the Price Elasticity of Computing the Price Elasticity of Demand Using the Midpoint Demand Using the Midpoint Formula Formula ◆例如,考虑下面的数字 For example, consider these numbers 当计算需求价格弹性时,中点公式更为可取,因 e Point A: Price=S4, Quantity=120 为无论变化的方向如何,它都能给出相同的答案 e Point B: Price=S6 Quantity=80 The midpoint formula is preferable when ◆弹性分别是 Elasticities are, calculating the price elasticity of demand because it gives the same answer regardless of the direction of ◆I(80-120)/120(6-4)/4|=(-33).5=-0.66 Price Elasticity of Demand=(Q-Q,)/(Q+Q)/2)1 ◆B→A: (P2-P1)/[(P2+P1)2] ◆l(120-8080/1(46)/6=5/(-33)=1.5 运用中点公式计算需求价格弹性 computing the Price Elasticity of 计算需求价格弹性 Demand Using the Midpoint Computing the Price Elasticity Formula of demand ◆在我们的例子中,A点和B点的中点是 Price Elasticity of Demand =(Qx-Qn/(Q 2+Q1/21 In our example, the mid point between point A 2-P1)[(P2+P1)2 and B is ◆中点 Midpoint:价格 Prices=S5,数量 Quantity=100 量从10个下降到个,运用中点公式,你的求弹性就可以计算如下 ◆无论方向,弹性均为1 S2.20 and the amount you buy falls from 10 to 8 cones, then your .A- in both directions equals I Elas elasticity of demand, using the midpoint formula, would be calculated ◆(80-120/100y(6-4)5=(-.2).2=1 (10+8)/2 ◆B→A: 22 percent=2.32 ◆(120-80/100(4-6)5}=,2/(-2)=1 (2.00+2.20)/22 计算需求价格弹性 Computing the Price Elasticity of Demand Percentage change in price Percentage change in quatity demanded Price elasticity of demand = 例：如果冰淇淋蛋卷的价格从2.00美元上升到2.20美元，你所购买 的数量从10个下降到8个，那么你的需求弹性可以计算如下： Example: If the price of an ice cream cone increases from $2.00 to $2.20 and the amount you buy falls from 10 to 8 cones then your elasticity of demand would be calculated as: (8 10) 100 10 20 2 (2.20 2.00) 10 100 2.00 percent percent − × − = =− − × 运用中点公式计算需求价格弹性 Computing the Price Elasticity of Demand Using the Midpoint Formula ‹ 如果你试图计算需求曲线上两点之间的需求价 格弹性，你马上就会注意到一个恼人的问题： 从A点到B点的弹性，与从B点到A点的弹性是 不同的。 If you try calculate the price elasticity of demand between two points on a demand curve, you will quickly notice an annoying problem: The elasticity from point A to point B seems different from the elasticity from point B to point A. 运用中点公式计算需求价格弹性 Computing the Price Elasticity of Demand Using the Midpoint Formula ‹ 例如，考虑下面的数字 For example, consider these numbers: ‹Point A: Price=$4, Quantity=120 ‹Point B: Price=$6, Quantity=80 ‹ 弹性分别是 Elasticities are, ‹A→B: ‹ [(80-120)/120]/[(6-4)/4] =(-.33)/.5=-0.66 ‹B →A: ‹[(120-80)/80]/[(4-6)/6]=.5/(-.33)=-1.5 运用中点公式计算需求价格弹性 Computing the Price Elasticity of Demand Using the Midpoint Formula 当计算需求价格弹性时，中点公式更为可取，因 为无论变化的方向如何，它都能给出相同的答案 The midpoint formula is preferable when calculating the price elasticity of demand because it gives the same answer regardless of the direction of the change. (P P )/[(P P )/2] (Q Q )/[(Q Q )/2] Price Elasticity of Demand= 2 1 2 1 2 1 2 1 − + − + 运用中点公式计算需求价格弹性 Computing the Price Elasticity of Demand Using the Midpoint Formula ‹ 在我们的例子中，A点和B点的中点是 In our example, the midpoint between point A and B is, ‹ 中点Midpoint:价格Price=$5, 数量Quantity=100. ‹ 无论方向，弹性均为1 Elasticity in both directions equals 1, ‹A→B: ‹ [(80-120)/100]/[(6-4)/5] =(-.2)/.2=-1 ‹B →A: ‹[(120-80)/100]/[(4-6)/5]=.2/(-.2)=-1 计算需求价格弹性 Computing the Price Elasticity of Demand 例：如果冰淇淋蛋卷的价格从2.00美元上升到2.20美元，而你购买的数 量从10个下降到8个，运用中点公式，你的需求弹性就可以计算如下： Example: If the price of an ice cream cone increases from $2.00 to $2.20 and the amount you buy falls from 10 to 8 cones, then your elasticity of demand, using the midpoint formula, would be calculated as: 2.32 9.5 22 (2.00 2.20)/ 2 (2.20 2.00) (10 8)/ 2 (10 8) = = + − + − percent percent (P P )/[(P P )/2] (Q Q )/[(Q Q )/2] Price Elasticity of Demand = 2 1 2 1 2 1 2 1 − + − +