问一道 GWD 数学题，有点不懂~ 谢谢大家！

bisujiangkai · 发表于 2009-11-2 21:43:05

Q14:

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)]

A. 1/4

B. 7/12

C. 2/3

D. 7/8

E. 8/7

选B，这题怎么做出来的？谢谢谢谢！

kosimon · 发表于 2009-11-2 22:00:24

设migrating geeses 为M只，原来有T只。
则按照题意，[Migration rate for geese of a certain sex = (number of geese of that sex migrating) / (total number of geese of that sex)]
可知，male geese 是0.2M/0.3T，而female geese为0.8M/0.7T,两式一除，M、T都被消去，就得7/12啦。

问一道 GWD 数学题，有点不懂~ 谢谢大家！

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