Spend an afternoon brushing up on statistics. Discover how the Krebs cycle works. Get a head start on next semester's geometry. Prepare for upcoming exams. Or, if you're feeling particularly adventurous, learn how fire-stick farming changes the landscape of Australia. Whether you're a student, teacher, homeschooler, principal, adult returning to the classroom after 20 years, or a friendly alien trying to get a leg up in earthly biology — Khan Academy's personalized learning library is available to you, for free. - Learn anything, for free: Thousands of interactive exercises, videos, and articles at your fingertips. Study math, science, economics, finance, grammar, history, government, politics, and much, much more. - Sharpen your skills: Practice exercises, quizzes, and tests with instant feedback and step-by-step hints. Follow along with what you're learning in school, or practice at your own pace. - Keep learning when you're offline: Bookmark and download your favorite content to watch videos without an internet connection. - Pick up where you left off: Tailored to your current learning level, our mastery system gives instant feedback and recommendations on exactly which skills and videos to try next. And, if you choose to create a free account, your learning syncs with http://khanacademy.org, so your progress is always up-to-date across all your devices. Learn using expert-created videos, interactive exercises, and in-depth articles in math (arithmetic, pre-algebra, algebra, geometry, trigonometry, statistics, calculus, differential equations, linear algebra), science (biology, chemistry, physics), economics (microeconomics, macroeconomics, finance and capital markets), humanities (art history, civics, finance, US history, US government and politics, world history), and more (including computer science principles)! Already familiar with the Khan Academy website? Not all functionality is available in this app. Community discussions, computer programming content, test prep, parent tools, teacher tools, and district tools should all be accessed directly at http://khanacademy.org. Khan Academy is a 501(c)(3) nonprofit organization, with the mission of providing a free, world-class education for anyone, anywhere.