PED作为开始学习AS经济后接触的第一个Elasticity，

其重要性不言而喻。

而且PED的知识中包括了比较多细小的内容，

需要同学们理解清楚后仔细区别记忆。

虽然知识并没有很复杂，

但是在AS以及A2的考试中，

都将会一直碰到需要它帮助分析解题的时候，

所以同学们要努力做到这块知识能够“信手拈来”，

这部分的知识基础打好了，

就不会丢掉考官拱手送上的分数。

(1)  PED=∞, perfectly elastic

Do not change the price or the total revenue will be zero

(2)  ∞>PED>1, relative elastic

Increase in price will result in more than proportionate decrease in quantity demanded,

which will cause total revenue to decrease.

Decrease in price will result in more thanproportionate increase in quantity demanded, 

which will cause total revenue toincrease.

(1)  PED=1, unitary elastic

Increase in price will result in the same percentage decrease in quantity demanded,

leaves the total revenue unchanged.

(1)  1>PED>0, relatively inelastic

Increase in price will result in less than proportionate decrease in quantity demanded,

so the total revenue increases. 

Decrease in price will result in less than proportionate increase in quantity demanded, 

so the total revenue decreases.

(2)  PED=0, perfectly inelastic

Increase in price results in no change in quantity demanded, and the total revenue increases.