Barron's "E-Z" books are self-help manuals focused to improve students' grades in a wide variety of academic and practical subjects. For most subjects, the level of difficulty ranges between high school and college - 101 standards. Although primarily designed as self-teaching manuals, these books are also preferred by many teachers as classroom supplements - and for some courses, as main textbooks. "E-Z" books review their subjects in detail, and feature both short quizzes and longer tests with answers to help students gauge their learning progress. Subject heads and key phrases are set in a second colour as an easy reference aid. This book explains probability, random variables, distributions, laws of large numbers and the central limit theorem, polls and sampling, linear regression, and much more. It provides hundreds of exercises with selected answers.