The price of a good falls from $15 to $13. Given this decline in price, the quantity demanded of the good rises from 100 units to 120 units. The own-price elasticity of demand for the good is closest to:
A –0.67.
B –1.50.
C –1.25.
这个题目为什么不用均值法？什么情况下用均值法？
