又来一个概率题！求帮忙！

本帖最后由 hell55 于 2011-9-24 16:32 编辑

1.A firm that makes T-shirt decals has determined that their process yields, on average, 3 defects per day. Fifty decals are inspected each day.
Q：What is the probability of buying a decal that contains more than 1 defect?

2.A parts dealer buys parts from a warehouse. Parts are made by either Company A or Company B but are not identified as to which company produces them. One company produces all parts in one shipment or lot. On the average, we know:
Company A produces 2.5% defective parts.
Company B produces 5.0% defective parts.
The warehouse states that 70% of parts will come from Company A and 30% from Company B. If the dealer selects 4 parts at random from a lot and finds 1 defective part, what is the probability that the lot was produced by Company A?

这个怎么算呀？糊涂啦！求高手帮忙呀！