在解概率问题时 ,有的同学见到公式就急忙套用 ,也不管题目是否具备运用公式的条件 ,结果容易导致错误 .例 1　已知A、B为两互斥事件 ,且P(A)=0 .3 ,P(B) =0 .5 ,试求P(A +B)与P(A·B) .错解　∵　P(A) =0 .3 ,　P(B) =0 .5 ,∴　P(A) =0 .7,　P(B) =0 .5 ,∴　P(A +B) =P(A) + When solving the probability problem, some of the students quickly applied the formula when they saw it, and regardless of whether the problem has the conditions to use the formula, the result is likely to lead to an error. Example 1 It is known that A and B are two mutually exclusive events, and P(A)= 0 .3 ,P(B) =0 .5, try P(A +B) and P(A·B). False solutions ∵ P(A) =0.3, P(B) =0.5, ∴ P(A) =0.7, P(B) =0.5, ∴ P(A +B) = P(A) +