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数学 关键是题没读懂 NN帮忙啊

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楼主
发表于 2009-6-5 17:50:00 | 只看该作者

数学 关键是题没读懂 NN帮忙啊

A total of 30 percent of the geese included in a certain migration study were male. If some of the geese migrated during the study and 20 percent of the migrating geese were male, what was the ratio of the migration rate for the male geese to the migration rate for the female geese? [Migration rate for geese of a certain sex = (number of geese of that sex migrating) / (total number of geese of that sex)] 1/4 7/12 2/3 7/8 8/7
沙发
发表于 2009-6-5 18:33:00 | 只看该作者

我不是NN,不过这道题好像做过,有点印象的。是不是选7/12?

题意是说,有一群鹅,公鹅占30%。在研究中,有一批鹅迁徙了,其中20%是公鹅。题目问公鹅迁徙率 比上 母鹅迁徙率。

我的做法是,设鹅的总数是X,迁徙的鹅总数是Y。由题目可知,母鹅数为70%X,迁徙的母鹅书为80%Y。公鹅的迁徙率为 迁徙的公鹅 比上 公鹅总数 20%Y/30%X。母鹅的迁徙率同理为 80%Y/70%X。 再把两者一除就出来了:2/3 除以 8/7 = 7/12

板凳
发表于 2009-6-5 18:45:00 | 只看该作者
对吧 migration ratio , m:f = 1:4, total ratio, m:f = 3:7 Hint中有公式啊 就直接用 (1:4)/(3:7) = 7/12  好像考的就是 (m:m)/(f:f)=(m:f)/(m:f)
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