题目一名学生每天骑自行车上学,从他家到学校的途中要经过4个交通岗.假设他在各交通岗遇到红灯的事件是相互独立的,并且概率都是14.(Ⅰ)求这名学生连续在两个交通岗遇到红灯的概率;(Ⅱ)设ξ是这名学生在遇到红灯前已经经过的交通岗数,求Eξ.错误解答(Ⅰ)P=3·(14)2·(1-14)2=27 Title A student rides a bicycle to school every day. From his home to school, he needs to pass through 4 traffic posts. It is assumed that the events he encounters with the red light at each traffic post are independent of each other, and the probabilities are all 14. (I) The student’s probability of encountering a red light continuously at two traffic posts; (II) The number of traffic posts the student had passed before the red light, asking Eξ. Wrong answer (I) P=3· (14)2(1-14)2=27