求助逻辑题一道

linchaoyi

Q14:
Smithtown University’s fund-raisers succeeded in getting donations from 80 percent of the potential donors they contacted.  This success rate, exceptionally high for university fund-raisers, does not indicate that they were doing a good job.  On the contrary, since the people most likely to donate are those who have donated in the past, good fund-raisers constantly try less-likely prospects in an effort to expand the donor base.  The high success rate shows insufficient canvassing effort.

Which of the following, if true, provides more support for the argument?

A.    Smithtown University’s fund-raisers were successful in their contacts with potential donors who had never given before about as frequently as were fund-raisers for other universities in their contacts with such people.
B.    This year the average size of the donations to Smithtown University from new donors when the university’s fund-raisers had contacted was larger than the average size of donations from donors who had given to the university before.
C.    This year most of the donations that came to Smithtown University from people who had previously donated to it were made without the university’s fund-raisers having made any contact with the donors.
D.    The majority of the donations that fund-raisers succeeded in getting for Smithtown University this year were from donors who had never given to the university before.
E.    More than half of the money raised by Smithtown University’s fund-raisers came from donors who had never previously donated to the university.
答案给的是A，真的是A吗？为什么啊。。。。求大神们详解。谢啦

rickylau77

十分感谢·····

linchaoyi

这其实是个数学题

前提：捐款来自于两个部分  从前捐钱的 和 从前不捐的 总成功率等于从前捐钱和不捐的的加权平均
即
总成功率= 从前捐钱的成功率* contacts with people who have donated in the past+ 从前不捐的成功率* contacts with potential donors who had never given before / 总contact数量

A 说 SU接触从前不捐的人的成功率和其它学校一样  
又由于题干中已经说明 接触从前捐钱的成功率高 且SM的总成功率最高
也就是说在SU的总成功率中 从前捐钱的权重更高 也可以说比例更高 因此 从前不捐的比例低 从而支持结论exceptionally high for university fund-raisers, does not indicate that they were doing a good job

B 捐款数量比原来多  无关
C 无关
D E 都是说来自从前没捐的多 是削弱结论的

-- by 会员 HarrisZheng (2012/1/4 14:18:03)

万分感谢同学你的解答！！！谢谢！！！！！！

HarrisZheng

这其实是个数学题

前提：捐款来自于两个部分  从前捐钱的 和 从前不捐的 总成功率等于从前捐钱和不捐的的加权平均
即
总成功率= 从前捐钱的成功率* contacts with people who have donated in the past+ 从前不捐的成功率* contacts with potential donors who had never given before / 总contact数量

A 说 SU接触从前不捐的人的成功率和其它学校一样  
又由于题干中已经说明 接触从前捐钱的成功率高 且SM的总成功率最高
也就是说在SU的总成功率中 从前捐钱的权重更高 也可以说比例更高 因此 从前不捐的比例低 从而支持结论exceptionally high for university fund-raisers, does not indicate that they were doing a good job

B 捐款数量比原来多  无关
C 无关
D E 都是说来自从前没捐的多 是削弱结论的