【PREP_DS】CD上没搜到的一题！求大侠指点！

mirrorsoda · 发表于 2011-10-7 16:36:14

Each of the students in a certain class received a single grade of P,F or I.What percent of the students in the class were female?

(1)Of those who received a P,40 percents in the class were females

(2)Of those who received either an F or I，80 percents were males

正确答案是E，我选择了C

shenqi45678 · 发表于 2011-10-7 16:59:43

同问，这种类型滴题目~~~

manxeon · 发表于 2011-10-7 19:30:41

没法推出班里有多少人得了P，还是无解

mirrorsoda · 发表于 2011-10-8 09:41:37

就是，不能把百分比相加除以2吗？

mirrorsoda · 发表于 2011-10-8 09:43:02

没法推出班里有多少人得了P，还是无解

-- by 会员 manxeon (2011/10/7 19:30:41)

就是不能百分比相加除以二吗？

不倒翁要杀鸡 · 发表于 2011-10-8 09:49:20

因为不知道P，F，I的比例。要是知道这个比例就能求出来了

renbin · 发表于 2011-10-8 10:08:25

我是这么想的，设班里一共有N个人，则得P的女生为40%P，得F或者I的女生为（N-P）80%，求女生占班级总人数的比例就是[40%P+（N-P）80%]/N，肯定解不出来，所以E

mirrorsoda · 发表于 2011-10-8 10:25:27

我是这么想的，设班里一共有N个人，则得P的女生为40%P，得F或者I的女生为（N-P）80%，求女生占班级总人数的比例就是[40%P+（N-P）80%]/N，肯定解不出来，所以E

-- by 会员 renbin (2011/10/8 10:08:25)

谢谢你们的回答！有好心人告诉我看og12P144，我看了后有些启发，但是感觉还是无法用这种方法做这个题目。
Example 2: In a certain production lot, 40 percent of the toys are red and the remaining toys are
green. Half of the toys are small and half are large. If 10 percent of the toys are red and small, and
40 toys are green and large, how many of the toys are red and large.
Solution: For this kind of problem, it is helpful to organize the information in a table:
Red Green Total
Small 10% 50%
Large 50%
Total 40% 60% 100%
Th e numbers in the table are the percentages given. Th e following percentages can be computed on
the basis of what is given:
Red Green Total
Small 10% 40% 50%
Large 30% 20% 50%
Total 40% 60% 100%
Since 20% of the number of toys (n) are green and large, 0.20n = 40 (40 toys are green and large), or
n = 200. Th erefore, 30% of the 200 toys, or (0.3)(200) = 60, are red and large.

mirrorsoda · 发表于 2011-10-8 10:28:40

因为不知道P，F，I的比例。要是知道这个比例就能求出来了

-- by 会员不倒翁要杀鸡 (2011/10/8 9:49:20)

谢谢！我大概懂了！非常感谢~可能我做题目的弱点在于，知道自己在哪个知识点上有漏洞，然后碰到类似的题目就傻眼吧。还真不符合GMAT所需要的“必要性思维”啊！呵呵，有待提升~

【PREP_DS】CD上没搜到的一题！求大侠指点！

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