[讨论]Feifei,No.70,NN来帮忙啊

tichondrius

A low-pressure weather system is approaching Plainville; rainfall results from about 70 percent of such systems in the Plainville area. Moreover, the current season, spring, is the time of year in which thundershowers, which sometimes result from low-pressure systems, are most likely to occur in Plainville.

 

Knowing which one of the following, in addition to the information above, would be most useful for determine the probability that Plainville will have a thundershower soon?

 

A.       the percentage of thundershowers in Plainville that occur in the spring

B.        the percentage of spring rainfalls in Plainville that are thundershowers

C.        the percentage of thundershowers in Plainville that result from low-pressure systems

D.       whether low-pressure systems in other areas are associated with rainfall

E.        whether Plainville has more or fewer thundershowers each spring than do near by towns

 

原文解释：C

思路：文中给出两个条件，1是低压天气将到达，而70%的低压天气导致降雨，2是现在正是1年中雷阵雨最多的季节且雷阵雨有时也是由于低压天气导致；答案（C）给出了低压天气导致雷阵雨的比率，用70%乘以这个比率，就可以得到下雷阵雨的概率了。

A、B没能和低压天气联系起来，D、E为无关选项

我到现在也没搞明白为什么这么算，我认为应该是70%的低压天气致降雨，乘以降雨就是雷阵雨的比例，才是P下雷阵雨的概率，也就是说低压必然来，那么就是1，1*70%是降水的概率，降水不一定是雷雨阿，再乘以一个降水是雷雨的概率，就是P要雷雨的概率。而C直接给出的就是低压天气导致雷阵雨的概率，还算什么。望指教。十分的不理解。