From Khan Academy:
Khan Academy allows you to learn almost anything for free. In our iPhone app: You can learn anything - for free: Over 10, 000 videos and explanations at your fingertips in math, science, economics, history, and much, much more. Sharpen your skills: over 40, 000 interactive Common Core aligned practice questions are included with instant feedback and step-by-step hints. Follow along with what you're learning in school or practice at your own pace. Quickly find what you need: Redesigned navigation and search make it faster to find what you want. Keep learning even when you're offline: Bookmark your favorite content to "Your List" for easy access, and download it to keep learning even when you're not connected to the internet. Pick up where you left off: Your learning syncs between your iPhone and khanacademy.org, so your progress is always up-to-date. In our iPad app, you can also: Flex your muscles: the app adjusts to give you interactive exercise recommendations that are tailored just for you through the world of math. Show your work: the app harnesses the power of writing down your thoughts as you problem-solve with a beautiful, expansive scratchpad. Once you have your answer, just write it in, and we'll recognize your handwriting (powered by MyScript). 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, and even the humanities with playlists on art history, civics, finance, and more. Spend an afternoon brushing up on statistics. Discover how the Krebs cycle works. Learn about the fundamentals of music notation. Prepare for the upcoming SAT, GMAT, or MCAT. Or, if you're feeling particularly adventurous, learn how fire stick farming changed the landscape of Australia. It doesn't matter if you are a student, teacher, home-schooler, principal, adult returning to the classroom after 20 years, or a friendly alien just trying to get a leg up in earthly biology--Khan Academy's materials and resources are available to you completely free of charge. Head over to www.khanacademy.org to learn more. "Khan Academy allows you to learn almost anything for free.