David Romer的《高级宏观经济学》的参考答案
Solutions to chapter  1
Problem 1.1
a) Since there is no technological progress, we can acrry out the entire analysis in terms of capital
 and output per worker rather than capital and output per unit of effective labor. With A constant, they
behave the same. Thus for the purpose of this problem we can define y=Y/L and k=K/L.
The fall in the population growth rate makes the break-even investment line flatter. In the absence
 of technological progress, the per unit time change in k, capital per worker, is given by k=sf(k)-(g+n)k.
 Since k was 0 before the decrease in n-the economy was on a balanced growth path-the decrease in n
causes k to become positive. At k*. actual investment per worker, sf(k*), now exceeds break-even invesdtment
 per worker, (nnew+g)k*. Thus k moves to a new higher balanced-growth-path level-see the diagram.