An experiment is designed to test the potency of a drug on 20 rats.

An experiment is designed to test the potency of a drug on 20 rats. Previous animal studies have shown that a 10-mg dose of the drug is lethal 5% of the time within the first 4 hours; of the animals alive at 4 hours, 10% will die in the next 4 hours. 4.46 What is the probability that 3 or more rats will die in the first 4 hours? 4.48 What is the probability that 0 rats will die in the 8-hour period? 4.50 What is the probability that 2 rats will die in the 8-hour period?