求助gwd的一到题

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

这题答案给的是B，小妹甚是不解，不知那位哥哥姐姐能指点一下！！~~

Can you chage the font a littler larger? I can hardly recognize.

the rotio is (20%/30%)/(80%/70%)=7/12