- "Free lecture notes, exams, and videos from MIT."
- "MIT OpenCourseWare (OCW) is a web-based publication of virtually all MIT course content."
- "Each course we publish requires an investment of $10,000-15,000 to compile course materials from faculty."
- "Last year alone, OCW received 17.5 million visits from 9.5 million individuals, and to date the site has been visited more than 75 million times by an estimated 45 million individuals."
Considering that there are close to 40 separate areas, the math part must have received about 500,000 visits in 2010.
For alternatives, see Math online.