1. The problem statement, all variables and given/known data Suppose i have 150 birds each having a survival rate of .5. 2. Relevant equations What would be the probability that there are 0 birds after 5 times steps? 3. The attempt at a solution The only way I could think of doing this would be to find the expected value after four time steps which would be 150*(.5)^4 = 4.6875. This would indicate that there are 4 birds left so I would find the probability 4 birds die in one time step which is .5^4. However, it is incorrect..