An experiment is designed to test potency of the drug on 20 rats. Previous animal studies have shown that the 10 mg dose of the drug is lethal 5% of the time in the fist 4 hours of the animals alive at four hours 10% will die in the next 4 hours. Determine the probability that three or more rats will die in the next four hours? Determine the probability that 0 rats will die in the 8 hour period?