（iv）Three students are chosen at random．Find the probability that exactly 1 is studying Music and exactly 2 are boys．
（iv）随机选择三个学生。求正好 1 个在学习音乐，正好 2 个是男生的概率。
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
（b）Find the total number of different arrangements of the 8 letters in the word TOMORROW that have an R at the beginning and an R at the end，and in which the three Os are not all together．
（b）查找单词 TOMORROW 中开头有 R，结尾有 R 的 8 个不同排列的字母的总数，其中三个 O 并不都在一起。
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad
$$$$qquad\qquad