题目

1.The weather forecaster says that there is 10% chance of rain for each day
a.What is the probability that it rains at least one of the next three days?
b.What is the probability that it will rain exactly 2 days of the next 14 days?Round to thousands.
2.9 students are chosen at random for the prom committee from a group that includes 5 sophomores,12 juniors,and 10 seniors.What is the probability that the committee will have 1 sophomore,5 juniors,and 3 seniors on it?
我理解两题意思是：1、天气预报说每天的降水概率为10％ a.未来三天内至少一天降水的概率为多少?b.未来十四天有两天降水的概率为多少?约到百分位.
2、9个学生被从一个有5个十年级生、12个十一年级生、10个十二年级生的团体里随机选出参加舞会委员会.那么刚好选出1个十年级生、5个十一年级生、3个十二年级生的概率为多少?

提问时间：2021-03-17

答案

1：a.1-（1-10%）^3=0.271 b.C(14 2)*10%^2*(1-10%)^2=0.257
2：C(5 1)*C(12 5)*C(10 3)/C(27 9)=0.101