I was just working with a student, and they had a probability problem where:

P(A or B) = 1/2, but P(B) = 3/4

This really isn't a context where P(A and not B) is allowed to be -1/4.

P(A or B) = 1/2, but P(B) = 3/4

This really isn't a context where P(A and not B) is allowed to be -1/4.

**Current Mood:**annoyed

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