How long would it take a running faucet to fill the inverted dome of the Capitol? What is the total length of all the pickles consumed in the US in one year? What are the relative merits of internal-combustion and electric cars, of coal and nuclear energy? The problems are marvelously diverse, yet the skills to solve them are the same. ** The conversion efficiency (the ratio of animal feed to animal weight) varies from two for chickens and fish through four for pork to seven for beef.