Author: Khan Academy via YouTube
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Khan Academy is a non profit organization supported by philanthropic donations. We are able to create interactive software, exercises, videos and articles for the world, for free because of this support. But we were already running at a deficit before the COVID-19 crisis and now our server load is 2.5x normal (approaching 100m learning minutes on Khan Academy *per day*). Please think about donating at http://khanacademy.org/donate

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