问题如下：
Emma sells homemade cakes in New York. Everyday she can sell 250 cakes with a price of $10. She offers special discount on Mother's day and expected to sell 350 cakes with a discounted price of $8. The marginal revenue per cake she sells from special discount is:
选项：
A. $3.
B. $2.
C. $2.5
解释：
A is correct.
Marginal revenue is the increase in total revenue from selling one more unit of a good. In this case, selling 100 more cakes increase the revenue of $300 (350*$8-250*$10), therefore the marginal revenue is $300/100=$3
考点：边际收益
解析：
首先求得总收益的增加量$300 (350*$8-250*$10)
再求得销售量的增加量100
之后套用公式：边际收益=总收益的增加÷产量的增加
$300/100=$3.
怎么理解这道题目呢？？
