Exercism
exercism.org
Practice exercises in 80-odd languages with free feedback from a human mentor
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khanacademy.org
Explains school maths and science one short video and one exercise at a time.
A complete maths spine from counting through early calculus, plus physics, chemistry, biology, economics and standardised-test prep, built as short videos followed by practice questions that adapt to what you get wrong. The mastery view is the part worth using: it shows which sub-skill is broken rather than just a score on a topic. Strongest for school-age material — the university-level and humanities content is much thinner than the maths.
Questions
Free to use, but you have to register before it will do the job. Watching is open but practice and progress tracking need a free account, and nothing here carries academic credit.
Yes. Khan Academy sends your input to its own servers to process it. That is fine for public material; for anything containing personal data, use one of the on-device tools instead.
Watching is open but practice and progress tracking need a free account, and nothing here carries academic credit.
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exercism.org
Practice exercises in 80-odd languages with free feedback from a human mentor
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