概率题,自己感觉有点小变态.

1.four machines,labeled A,B,Cand C, are used to produce golf balls. Of the total output, Machine produces 10%, B 20%, C 30%, D 40%, of the golf balls produce by machineA, %1 are defective; by machine B, 2%, by machine C3% , and D4%

Question: what proportions of the golf balls are defective? Given that a ball is defective, what is the probability that machine D made it? Given that a ball is defective, what is the probability that machine A did not make it.

2.A sakesman has a 30% probability of making a sale to any customer. Assume all customers are independent of one another.

Question: What is the probability the first sale is made to the third customer? what is the probability the first four customers do not purchase the product?

大家帮帮忙,要不又该睡不着了.小弟感激不尽