我知道后面的加法法则，但还是有点没懂p23和p25怎么算的

NO.PZ2018062016000091 问题如下 Given a screte ranm variable Y, the set of all the possible Y value is Y = {20,21,22,23,24,25}.The estimatevalue of cumulative stribution function is in the table, whis the probability thY takes 23 or 25? A.0.50 B.0.45 C.0.75 A is correct. F(23) = P(Y≤ 23) = p(20) + p(21) + p(22) + p(23) = 0.55. F(22) = P(Y≤ 22) = p(20) + p(21) + p(22) = 0.30. So p(23) = 0.55-0.30 = 0.25. For the same reason, F(25) = 1.00, F(24) = 0.75, p(25) = 1.00-0.75 = 0.25.The probability thY takes 23 or 25 = p(23) + p(25) = 0.25+0.25 = 0.50 还是没看懂题，怎么看是求得是 1-p 而不是三个标准差呢

NO.PZ2018062016000091 问题如下 Given a screte ranm variable Y, the set of all the possible Y value is Y = {20,21,22,23,24,25}.The estimatevalue of cumulative stribution function is in the table, whis the probability thY takes 23 or 25? A.0.50 B.0.45 C.0.75 A is correct. F(23) = P(Y≤ 23) = p(20) + p(21) + p(22) + p(23) = 0.55. F(22) = P(Y≤ 22) = p(20) + p(21) + p(22) = 0.30. So p(23) = 0.55-0.30 = 0.25. For the same reason, F(25) = 1.00, F(24) = 0.75, p(25) = 1.00-0.75 = 0.25.The probability thY takes 23 or 25 = p(23) + p(25) = 0.25+0.25 = 0.50 本题中为什么P（23）和P（25）属于互斥事件 如何判断互斥事件的情况

NO.PZ2018062016000091 请问，本题的问法是否错误，应该是P（23）anp(25)吧，而不是or

NO.PZ2018062016000091 0.45 0.75 A is correct.  F(23) = P(Y≤ 23) = p(20) + p(21) + p(22) + p(23) = 0.55. F(22) = P(Y≤ 22) = p(20) + p(21) + p(22) = 0.30. So p(23) = 0.55-0.30 = 0.25. For the same reason, F(25) = 1.00, F(24) = 0.75, p(25) = 1.00-0.75 = 0.25. The probability thY takes 23 or 25 = p(23) + p(25) = 0.25+0.25 = 0.50老师，这个取到23或25的概率不可以用加法法则吗（两个至少取到一个的概率） 就是(0.25+0.25)-0.25*0.25