Posted by
**Cathy** on
.

Test the potency of a drug on 20 rats. Previous animal show that a 10-mg dose of drug is lethal 5% of the time within 1st 4 hours; of the animals alive at 4 hours, 10% will die in the next 4 hours. What is the probability that 3 or more rats will die in the first 4 hours.