ALevel考试科目众多，包括数理化这些常见的科目，也包含了ALevel经济这样的热门科目，所以对于想要选择经济的考生来说，备考也显得相对困难，下面小编就带着大家学习ALevel经济中需求的交叉弹性！
小编建议大家要经常模拟分析并且推出相关结论，这样对考试中遇到类似问题后的思考过程很有帮助。
▎Cross elasticity of demand的定义为：
It measures the responsiveness of quantity demanded of a product A when there is a change in the price of a related product B。
也就是说，当product B的价格发生变化时，将会对product A的需求数量造成多大的影响。
▎计算公式为:
% Of change in quantity demanded of product A / % of change in the price of a related product B。
这里XED的value分为两种情况讨论，一种是相互为Complements的products，比如CD player和CD。
When the price of CD player decreases,
The quantity demanded for CD player and CD both increase；
When the price of CD player increases,
The quantity demanded for CDplayer and CD both decrease.
因为互为补足物的商品，如果其中一件商品的价格上涨，两者的需求数量将会同时下跌，反之亦然。
所以，Complements的XED value一定会是Negative的。
另一种是相互为Substitutes的products，比如Apple juice和orange juice。
When the price of apple juice increases,
The quantitydemanded for it will decrease,
And the quantity demanded for the relatively cheaper orange juice will increase;
When the price of apple juice decreases,
The quantity demanded for it will increase,
And the quantity demanded for the relatively more expensive
Orange juice will decrease.
互为替代品的商品，如果一种商品的价格上涨，另一种商品的价格将会变得相对便宜，而相对便宜的商品的需求数量将会上涨，另一个则会降低。所以，Substitutes的XED value一定会是positive的。
综上所述，通过XED value的正负号，我们也可以得知两个Products之间的关系了。
同时，根据XED value的绝对值大小，又可以将其分成四类。（以下数字全部为Assumption）
(1) XED=-3 (Elastic)
Two products are close compliments,
Such as: CD playerand CD.
(2) XED=-0.2 (Inelastic)
Two products are distant compliments,
Such as red wine and cheese.
(3) XED=2.6 (Elastic)
Two products are close substitutes,
Such as pepsi and coke.
(4) XED=0.3 (Inelastic)
Two products are distant substitutes,
Such as mineralwater and beer.
According to the extent(absolute value) of XED,
How closely the two products are related can be determined.
关于ALevel经济考试的考点就总结到这里了，希望考生们重视起来，除此之外，大家也要重视真题训练，打好备考技巧的基础。如果想要了解更多关于alevel培训哪家好、alevel评分标准等更多信息，大家可以线上咨询我们或继续关注网站更新的文章！
