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！ | 
