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OG12上，有一个题如下
Of the companies surveyed about the skills they
required in prospective employees, 20 percent
required both computer skills and writing skills. What
percent of the companies surveyed required neither
computer skills nor writing skills?
(1) Of those companies surveyed that required
computer skills, half required writing skills.
(2) 45 percent of the companies surveyed required
writing skills but not computer skills.
OG给的解释如下，
The surveyed companies could be placed into one
of the following four categories:
1. Requiring computer skills and requiring writing
skills
2. Requiring computer skills but not requiring
writing skills
3. Not requiring computer skills but requiring
writing skills
4. Not requiring either computer skills or writing
skills
It is given that 20 percent of the surveyed
companies fell into category 1. It is necessary to
determine what percent of the surveyed
companies fell into category 4.
(1) This helps identify the percentage in
category 2. Since 1/2 the companies that required
computer skills also required writing skills
(i.e., those in category 1), then the other 1/2
of the companies that required computer skills
did not require writing skills (thus category 2 =
category 1). However, this information only
establishes that 20 percent required computer
skills, but not writing skills; NOT sufficient.
我理解的条件（1）就是说，对于被调查的公司中，一些要求计算机技能（假设数量为C），其中一半于数量“C”要求写作技能（假设数量为W）。换句话讲，我理解的是C=2W，也就是说，有两种可能性（一种是，以C=20%为标准，W=10%；另一种是，为W=20%为标准，C=40%）。可是答案里说，因为一半的公司既要求计算机技能，又要求写作技能，所以另外一半的公司要求计算机技能不要求写作技能，所以category 2 = category 1，也就是说category 2也是20%。这个我没理解，为什么？请好心人帮忙解答一下，谢谢！ |
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发表于 2010-4-6 07:35:52
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