题目

在一袋中有一只红球和九只白球，每次从袋中取出一球记下颜色后放回，求取得红球次数ξ的分布列. 答案：解析：取得红球次数ξ的值为0、1、3、…、n，由于每次取球相互独立且“环境”相同，所以可以看成是n次独立重复试验，故服从二项分布ξ—B(n,0.1).∴P(ξ=k)=  (0.1)k×0.9n-k,故ξ的分布列为：ξ01…nP (0.1)0×0.9n0.1×0.9n-1…0.1n×(0.9)0用括号内所给动词的适当形式填空（用will构成的一般将来时）。1. My mother ________ (go) to Beijing tomorrow.2. He ________ (take) the bus to school next week.3. There ________ (be) a basketball match next Sunday.4. Mary ________ (visit) his grandparents the day after tomorrow.5. They ________ (watch) TV at home this weekend.6. Who ________ (help) you tomorrow?7. Mike ________ (clean) the room next day.8. ________ you ________ (read) the book in the future?9. What ________ she ________ (do) when she grows up?10. ________ you ________ (sing) the song soon?