The number of species in some endangered populationmay increase by one unit or decrease by one unit in one year with equal probability½ and independently from previous years.  

a)      a) Findnumerically the probability of the population surviving for 8 years if at thestarting moment the population was at the unit number 1.

b)      b) Estimatethe probability of the population surviving for 8 years with a return at year 8strictly to consist of only 1 unit.  

c)      c) Describeand estimate the probability of the population surviving for 32 years with a returnto consist of only one unit at the each of years 8, 16, 24, 32.