Y(1+r)^20 r=0. 05 (growth rate) small variation of growth rate will be a huge part get amount it will take to double your initial amount. Explaining the large variation in living standards around the world is, in one sense, very easy. Productivity: the quantity of goods and services produced from each hour of a worker"s time. Physical capital: the stock of equipment and structures that are used to produce goods and services: machines built, producing other goods. Human capital: the knowledge and skills that workers acquire through education, training, and experience: accumulate more and more machines that help us produce more, supposed to invest in order to get better. Natural resources: the inputs into the production of goods and services that are produced by nature, such as land, rivers, and mineral deposits o. Technological knowledge: society"s understanding of the best ways to produce goods and services: some kind of common knowledge we have as a society for being more productive o.