Dart Board Probability On a Dart board, with different areas labeled as: A, B, C, D, and each area different sizes.  The probabilities of each area are:  P(A)=25%, P(B)=50%, P(C)=12.5% and P(D)=12.5% 
What is P(~C or B)?  
I don't understand the "not C or B" term.  If it is not C then it includes B already. My guess would be 87.5%

You understood it correctly.  Besides recognizing that mathematically "or" includes both being true, another point was to read it as P((~C) or B) as opposed to P(~(C or B)), which would be 37.5%
