一道XDF的概率题

yue_1100

Forty percent of rats included in an experiment were male rats. If some of the rats died during the experiment, 30 percent of the rats that died were male rats, what was the ratio of death rate among the male rats to the death rate among female rats?

a. 9/14    b. 3/4   c. 9/11   d. 6/7    e. 7/8

答案是A,可我怎么算都觉得缺条件啊。望各位大牛指教！

atc

MM，把题目看清楚就可以啦 ,求thedeath rate among the male rats /the death rate among female rats

设总共有X参加实验，死了Y

有0.6X  FEMAL RATS，0.4X MALE RATS  死0.3Y MALE RATS 0.7Y FEMALE RATS

有0.3Y /0.4X /（0.7Y /0.6X）=9/14

yue_1100

以下是引用atc在2007-11-23 16:01:00的发言：

MM，把题目看清楚就可以啦 ,求thedeath rate among the male rats /the death rate among female rats

设总共有X参加实验，死了Y

有0.6X  FEMAL RATS，0.4X MALE RATS  死0.3Y MALE RATS 0.7Y FEMALE RATS

有0.3Y /0.4X /（0.7Y /0.6X）=9/14

太感谢了！！！我把相除的关系想成相乘的关系了。恍然大悟！

太谢谢了！！！！！