（b）The random variable $X$$X$XX has a normal distribution with mean equal to the standard deviation．Find the probability that a particular value of $X$$X$XX is less than 1.5 times the mean．
（b） 随机变量 $X$$X$XX 呈正态分布，均值等于标准差，求特定值 $X$$X$XX 小于均值的 1.5 倍的概率。
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4 Find the number of different arrangements that can be made of all 9 letters in the word CAMERAMAN in each of the following cases．
4 查找在以下每种情况下，单词 CAMERAMAN 中所有 9 个字母可以进行的不同排列的数量。
（i）There are no restrictions．
（i） 没有限制。
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（ii）The As occupy the 1st，5th and 9th positions．
（ii）依次占据第1、5、9位。
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（iii）There is exactly one letter between the Ms．
（iii） 两位女士之间正好有一个字母。
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