According to the Forbes article, tenured professors made up 17% of college classroom professors. A large portion of the other 83% live something like this: http://www.npr.org/2013/09/22/224946206/adjunct-professor-dies-destitute-then-sparks-debate

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After 25 years of teaching French at Duquesne, the university had not renewed her contract. As a part-time professor, she had been earning about $10,000 a year, and had no health insurance.