FeiFei-70

[CherrieLi]

70. 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

答案是C, 看了解釋還是不懂為什麼, 請大家幫忙提點一下....

原來解釋:

思路：文中給出兩個條件，1是低壓天氣將到達，而70%的低壓天氣導致降雨，2是現在正是1年中雷陣雨最多的季節且雷陣雨有時也是由於低壓天氣導致；答案（C）給出了低壓天氣導致雷陣雨的比率，用70%乘以這個比率，就可以得到下雷陣雨的概率了。