问题
单项选择题
Forty percent of the rats included in an experiment were male rats. If some of the rats died during the experiment and 30 percent of the rats that died were male rats, what was the ratio of the death rate among the male rats to the death rate among the female rats ？（）
A.A
B.B
C.C
D.D
E.E
答案
参考答案：A
解析：
设这些老鼠的死,亡的百分比为x，则雄性老鼠的死亡率为：
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雌性老鼠的死亡率为：
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所以雄雌死亡率的比率为：
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