求助GWD数学第六套Q14

小毅思

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

都不知道题目里的migrate的部分占总的geese的多少，怎么可能算出B的答案啊？求教。

ghpeng

设所有的geese是100， Male geese 是30， Female是70，设migration geese 总数为X, 其是20%*X是male geese, 80%*X 是female, migration male geese 占male geese的比率是：20%*X/30, migration female geese 占female geese的比率是：80%*X/70,二者相比得7/12

小毅思

自己顶。