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

设迁徙的共有X只鸟,那么迁徙的就有0.2X只雄鸟, 0.8只雌鸟.

而原来的时候有30只雄鸟,70只雌鸟(设总数为100)

根据题目给出的公式计算:

结果:   (0.2X/30)/(0.8X/70)=7/12, B