在化工产业的企业总体中,令rd表示年研发支出,sales表示年销售额(都以百万美元计)。
(i)写一个模型(不是估计方程),其中rd和sales之间的弹性为常数。哪一个参数代表弹性?
(ii)再用RDCHEM.RAW中的数据估计模型。用通常的形式写出估计方程。rd关于sales的弹性估计值是多少?用文字解释这个弹性的含义。
a. $100,000
b. $1,000
c. $100
d. $10,000
某次动物实验中测知,施用于动物的药物在其血液中的浓度逐天递减.用每百万个单位占多少个单位(ppm)度量的依度见下表.
(1)试构建药物浓度水平与所经历的时间之间关系的数学模型.
(2)用你的模型预测何时浓度水平会低于10ppm.
In 1998, the total demand for U. S. wheat was QD=3244-283P and the domestic supply was QS= 1944 + 207P. At the end of 1998, both Brazil and Indonesia opened their wheal markets lo U. S. farmers. Suppose that these new markets add 200 million bushels of U. S. wheat. What will the free - market price of wheat have been and what quantity would have been produced and sold by U. S. farmers?
此题为判断题(对,错)。