Question

大学数学概率问题，在线求解，急急急急

Suppose that a car salesman sells one or more cars on 65 percent of weekdays, and that the
outcomes on dierent days are independent of one another.
(a) What is the probability that the car salesman sells one or more cars on at least 3 of
the 5 weekdays next week?
(b) What is the probability that Thursday will be the second weekday next week on which
the car salesman sells one or more cars?

Answer 1

a)设一天一辆也卖不出去的概率是x，则1-x^5=0.65,所以x=0.35^0.2;
三天至少卖出一辆的概率为1-x^3=1-(0.35^0.2)^3=0.467。
b)周一至周三至少卖出一辆的概率为（1-x^3），乘以周四至少卖出一辆的概率（1-x），即为所求。（1-x^3)*(1-x)=(1-(0.35^0.3)^3)*(1-x)=0.304。