Khan Academy

Spend an afternoon brushing up on statistics. Discover how the Krebs cycle works. Learn about the fundamentals of music notation. Get a head start on next semester's geometry fundamentals. Prepare for the SAT, GMAT, LSAT, MCAT, NCLEX-RN, and AP 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 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: Your learning syncs with khanacademy.org, so your progress is always up-to-date.
Learn using videos, interactive exercises, and in-depth articles in math (arithmetic, pre-algebra, algebra, geometry, trigonometry, statistics, calculus, linear algebra), science (biology, chemistry, physics), economics (microeconomics, macroeconomics), humanities (art history, civics, finance, US history, US government and politics, world history), and more (including computer science principles)!
Khan Academy is a 501(c)(3) nonprofit organization, with the mission of providing a free, world-class education for anyone, anywhere.