This study analyzes the law of demand and supply, explores theories and models in contemporary economics, and their relation to the 20th century. It provides insights into the movement and change in demand and supply lines, factors affecting them, and their impact on business practice. The study also discusses Keynes' General Theory, classical microeconomics, Marxism, and other models. Subject: Economics, Course Code: N/A, Course Name: N/A, College/University: N/A