请教一道TTMath6中没看懂意思的题目

marco_polo

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

Answer: B

------------------------------------------------------------------------------------------------------------

请高人解释一下

davyzhu

设总数为100，其中male 30,female 70

迁徙总数为x，其中male 0.2x, female 0.8x

那么male的迁徙比例和female的迁徙比例之比：

0.2x/30  :  0.8x/70     =7/12

殇阳雪

设一共有100个geese in this study, 则30个male 70个female, 假设50个geese migrated during the study,则其中10个male,40个female . so the ratio of the migration rate for the male geese to the migration rate for the female geese is (10/30)/(40/70) 则选B

麻烦了一点哈.