GWD2-14

静夜

A total of 30% of the geese included in a certain migration study were male. If some of the geese migrated during the study and 20% 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

给我整糊涂了...我选的A,答案是B...请高手们指点一下!谢谢!

satancn

不是高手 设Male=30 Female=70 m=migrated

migrated male=m*20%, migrated female=m*80%

answer=(20%m/30)/(80%m/70)=7/12

静夜

多谢~~短路了~~