Final answer:
Eli Whitney's two important inventions were the cotton gin and interchangeable parts, which revolutionized the cotton industry and manufacturing processes.
Step-by-step explanation:
Eli Whitney invented two important inventions, the cotton gin and the concept of interchangeable parts. The cotton gin revolutionized the cotton industry by removing seeds from cotton fibers more quickly than by hand, making cotton production faster and more efficient. The concept of interchangeable parts allowed for the mass production of goods by making it easier to replace broken parts with identical ones, leading to increased efficiency and standardized production.