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题库 / GMATLA-PS-115
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)]
~$\frac{1}{4}$~
~$\frac{7}{12}$~
~$\frac{2}{3}$~
~$\frac{7}{8}$~
~$\frac{8}{7}$~
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总数有y只鹅，其中雌鹅有0.3y只，雄鹅有0.7y只。迁徙的鹅有x只，其中雌鹅有0.2x只，雄鹅有0.8x只。雌鹅的迁徙率为0.2x/0.3y，雄鹅的迁徙率为0.8x/0.7y。然后再把两个迁徙率想比就得出结果了
Let there be g geese, of which 0.3g are male and 0.7g are female
Lets say m geese migrated, 0.2m are male and 0.8m are female
Migration Rate Male = 0.2m / 0.3g = (2/3)*(m/g)
Migration Rate Female = 0.8m / 0.7g = (8/7)*(m/g)
Ratio of migration rates = (2/3) / (8/7) = 7/12