Alfred Marshall (1842-1924) was one of the most influential economists of his generation. His book, Principles of Political Economy (1890) brought together the theories of supply and demand, marginal utility and the costs of production[?] into a coherent whole. It was the dominant textbook in England for a long period.
... is spread out with 24.7% under the age of 18, 6.9% from 18 to 24, 36.3% from 25 to 44, 25.1% from 45 to 64, and 7.0% who are 65 years of age or older. The median age is ...