Sixty percent of the rats included in a particular experiment were female rats. If some of the rats died during the experiment and 30% of rats died were male, what was the ratio of the death rate among the male rats to the death rate among the female rats?

Let the number of rats be x.
Then, Number of female rats = 60% of x = 0.6x
Number of male rats = 40% of x = 0.4x
Let the number of rats that dies be y.
Then, Number of male rats that died = 30% of y = 0.3y
Number of female rats that died = 70% of y = 0.7y
Death rate of male rats = $$\dfrac{0.3y}{0.4x} = \dfrac{3y}{4x}$$

Death rate of female rats = $$\dfrac{0.7y}{0.6x} = \dfrac{7y}{6x}$$

Required ratio = $$\dfrac{3y}{4x} : \dfrac{7y}{6x} = 18 : 28 = 9 : 14$$