Mean, median, mode. The story of a population's heart. Standard deviation. The story of its anxiety, its dispersion, its beautiful, chaotic rebellion against the average. Regression analysis. The story of one thing whispering to another: I cause you. I predict you. I am your shadow.
Typically, the "solution pdf" refers to the Instructor's Solutions Manual or a Student's Solutions Manual. These documents contain step-by-step worked-out solutions to the even-numbered problems (which are often the ones assigned for homework, as odd-numbered answers are usually found in the back of the book). Mean, median, mode