# 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 did understand the term. The required probability is indeed $0.875$. The mathematical "or" is not quite the ordinary language "or." The event $X$ or $Y$ occurs if $X$ occurs or $Y$ occurs or both occur. Sep 22, 2013 at 15:57
• Think of it in terms of sets. Then 'or' becomes $\cup$ and 'and' becomes $\cap$. Hence you have $C^c \cup B = C^c$, since $B \subset C^c$. Sep 22, 2013 at 16:23