# (solution) please do question 1 and 3 ONLY. Slight change in question 1,

please do question 1 and 3 ONLY. Slight change in question 1, please use the production function of A x KL/K+L

ECON 100C: Midterm exam #1
October 15, 2015, 7pm-8:20pm
Show all work to receive full credit 1 Problem 1: Income di¤erences between US
and South Africa
Consider the simple production model where the aggregate production function takes the form:
p
(1)
F (K; L) = A KL with A &gt; 0;
where K denotes the capital stock rented by ?rms and L denotes the number
of workers hired by ?rms.
(i) Does this production function exhibit constant returns to scale? Justify
your answer. (ii) Write down the expressions for the wage and the rental price of capital
as a function of the capital stock per worker. (Make sure to explain where
these expressions come from.)
What is the value for the share of GDP paid to labor, also called &quot;labor
share&quot;? Is it consistent with the evidence for the US economy? 2 (iii) Express per capita GDP as a function of capital per person.
Draw a graphical representation of this relationship with capital per person on the horizontal axis and per capita GDP on the vertical axis. 3 (iv) According to Table 4.3 in your textbook the observed capital per person
in South Africa is equal to 16% the level in the US. The observed per capita
GDP is 18% the one in the US. Assuming South Africa and the US have
access to the same technology represented by (1), with the same TFP A, can
the production model account for the di¤erence of income between South
Africa and the US? Explain. (v) Normalize A = 1 for the US. What is the implied Total Factor Productivity for South Africa such that the observed per capita GDP and capital
per person are consistent with the production model? 4 Problem 2: Why do some countries produce
so much more output per worker than others?
In their 1999 article Robert Hall and Charles Jones use a version of the
production model where the production function takes the following form:
Y = K 1=3 (AhL)2=3 ; (2) where K denotes the stock of physical capital, h represents human capital
per worker (which increases with years of schooling), L is labor, and A is a
labor-augmenting measure of productivity.
(i) Explain the choice of the exponents, 1/3 and 2/3, in the production
function (2). (ii) Is it possible to rewrite the production function, (2), to make it similar
to the one used in the lecture, namely Y = AK 1=3 L2=3 ? 5 (iii) Show that output per worker, y = Y =L, can be expressed as:
Y
y=
=
L K
Y 1
2 where K=Y is the capital/output ratio. (HINT: Show ?rst that
K
AhL 1
3 and then compute Y =AhL.) 6 (3) Ah;
K
Y 1
2 = (iv) Robert Hall and Charles Jones report the following observations for the
year 1988.
country
U.S.
France
Mexico
China y
1.000
0.818
0.433
0.060 K 1=2
Y 1.000
1.091
0.868
0.891 h
A
1.000 1.000
0.666
0.538
0.632 Use Equation (3) to compute the implied productivity for the countries
in the Table above.
Based on this table how do you explain that China is so much poorer
than other countries in 1988? 7 Problem 3: Solow growth model
Consider a version of the Solow growth model where the aggregate production
function is:
p
Y = A KL:
We normalize the labor force to L = 1 and we assume that aggregate consumption is:
C = cY;
where c 2 (0; 1) the propensity to consume out of income. The depreciation
rate of capital is d.
(i) Write down the law of motion of the capital stock.
(You must obtain an equation with Kt+1 and Kt as the only endogenous
variables). 8 (ii) Give the expression for the steady-state capital stock.
Provide a graphical representation of the determination of the steadystate capital stock.
What is the e¤ect of an increase in c on capital and output? Explain. 9 (iii) Write down the closed-form solutions for output and consumption at the 