在美国，资本在GDP中的份额为30%左右；产出的平均增长为每年3%左右；折旧率为每年4%左右；资本—产出比率为2.5左右。假设生产函数是柯布—道格拉斯生产函数，因此，资本在产出中的份额是不变的，而且，美国已经处于稳定状态。

a．在初始稳定状态，储蓄率应该是多少？[提示：使用稳定状态的关系式：sy=(δ+n+g)k]

b．在初始稳定状态，资本的边际产量是多少？

c．假设公共政策提高了储蓄率，从而使经济达到了资本的黄金律水平。在黄金律稳定状态，资本的边际产量将是多少？比较黄金稳定状态的边际产量和初始稳定状态的边际产量，并解释。

d．在黄金律稳定状态，资本—产出比率将是多少？(提示：对柯布—道格拉斯生产函数来说，资本—产出比率与资本的边际产量是相关的。)

e．要达到黄金律稳定状态，储蓄率必须是多少？

In the United States, the capital share of GDP is about 30 percent; the average growth in output is about 3 percent per year; the depreciation rate is about 4 percent per year; and the capital-output ratio is about 2.5. Suppose that the production function is Cobb-Douglas, So that the capital share in output is constant, and that the United States has been in a steady state.

a．What must the saving rate be in the initial steady state？ [Hint: Use the steady-state relationship, sy=(δ+n+g)k]

b．What is the marginal product of capital in the initial steady state？

c．Suppose that public policy raises the saving rate So that the economy reaches the Golden Rule level of capital. What will the marginal product of capital be at the Golden Rule steady state？ Compare the marginal product at the Golden Rule steady state to the marginal product in the initial steady state. Explain.

d．What will the capital-output ratio be at the Golden Rule steady state？ (Hint: For the Cobb-Douglas production function, the capital-output ratio is related to the marginal product of capital.)

e．What must the saving rate be to reach the Golden Rule steady state？