Which of the four government policies to stimulate saving is essential? That is, which policy can on its own, regardless of the other policies, determine the level of the national saving rate?

How does the centrality of institutions and property rights in economic growth help to explain the predominance of rich countries in temperate climates and of poor countries in the tropics?

Suppose a wave of immigration increases the number of workers in research and development without altering the labor input in production. Describe the impact on the level and growth rate of output per worker, immediately, and as time passes.