800score中的一道逻辑题，求教！

ssissi · 发表于 2011-1-4 13:57:44

In a monogamous culture, 90% of the adults are married. The average number of children per family is five and over-population is a threat. Programs to encourage birth-control have been ineffective. It has been suggested that this failure is due to these programs ignoring a tradition that values male children very highly, so that every parent wants to have at least one son. It is proposed that couples be encouraged to use birth-control measures after the birth of their first son.

If this proposal is widely accepted in the culture, we may expect that:

A) the rate of population increase will be slowed, and future generations will contain a disproportionately high number of females.

B) the rate of population increase will be slowed, and the gender balance in future generations will remain as it is at present.

C) the rate of population growth will remain the same, and future generations will contain a disproportionately high number of females.

D) there will be no significant effect either on population growth or on gender balance.

E) the population will decline precipitously, because approximately half of all families will have only a single child.

答案是B。

不懂了，按照生男生女均为50%均等机会，但生到儿子的停止生育，生到女儿的继续生……这是个啥结果啊？

melvinperson · 发表于 2011-1-4 14:16:18

LZ 我是这么理解的

前提 <没有birth control>
男女出生比例各50% 人口会爆棚男女比例还是维持在50%左右（因为他们想要at least one son)

直接前提 <第一个男孩出生之后用birth control>

推断conclusion
1。birth control会降低人口增长；
2. 再细分
(a)50% 的家庭第一个孩子就是男孩，男孩=100% 女孩=0%
(b) 另外50%家庭第一到第N个孩子是全是女孩，第N+1个是男孩，男孩比例<=50% 女孩>=50%

把2(a)与2(b)综合一下结果表明男女比例维持原状

不知道我这样理解对不对

ssissi · 发表于 2011-1-4 14:29:52

半懂不懂，但还是谢谢melvinperson!

Lacus · 发表于 2011-1-4 18:52:12

这道题更像数学而不像逻辑。
人口增长率降低应该好理解，毕竟只要一生男就不再生了么。
如果有个前提条件，说生男生女的概率是均等的，那么由于每次生育的结果都是一半男一半女，所以性别比例不会变化。
但这个题没有该条件，是我想当然拿来用的，所以我没法确定这么做一定对。

melvinperson · 发表于 2011-1-6 07:25:35

我个人觉得这种题就是烦阿考试的时候我宁愿随便看看选个差不多的估计不会深究太浪费时间了

forgivexinian · 发表于 2011-1-8 14:46:26

样本足够大的时候，男女出生率就是1：1，可以把全城的家庭放在一起看。
而且就算不是，推行一个新政策也不会影响原本男女出生率的改变啊。总不能说现在政府说了两句话，于是大家生男孩的概率就增加了。所以就算以前是a ：b，现在也还是a：b。

800score中的一道逻辑题，求教！

所属分类: GMAT考试

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