题目

（北京卷理17）甲、乙等五名奥运志愿者被随机地分到四个不同的岗位服务，每个岗位至少有一名志愿者． （Ⅰ）求甲、乙两人同时参加岗位服务的概率； （Ⅱ）求甲、乙两人不在同一个岗位服务的概率； （Ⅲ）设随机变量为这五名志愿者中参加岗位服务的人数，求的分布列． 答案：【标准答案】: 解：（Ⅰ）记甲、乙两人同时参加岗位服务为事件，那么， 即甲、乙两人同时参加岗位服务的概率是． （Ⅱ）记甲、乙两人同时参加同一岗位服务为事件，那么， 所以，甲、乙两人不在同一岗位服务的概率是． （Ⅲ）随机变量可能取的值为1，2．事件“”是指有两人同时参加岗位服务I’m Kitty. I’m going to the to buy several things. On the first floor, I’m going to buy some , because my grandma likes fruits. The fruits are cheap and . I also want to buy some flour (面粉) because I want to biscuits. It is not easy but I want to . On the second floor, I want to buy some eggs. They are price on Friday. The normal price is 12 yuan a kilo but today is yuan. On the third floor, I want to buy a jacket my father. I know he likes blue I don’t know his size. I’ll call my mother and ask about it. I think my father will be happy with my present. 1.A. zoo B. cinema C. hospital D. supermarket 2.A. gloves B. flowers C. clothes D. bananas 3.A. bad B. strange C. fresh D. strong 4.A. buy B. post C. make D. eat 5.A. try B. turn C. get D. collect6.A. right B. high C. nice D. half7.A. 5 B. 6 C. 3 D. 48.A. with B. for C. in D. to9.A. or B. so C. anyway D. but10.A. you B. her C. you D. him