A random sample of size n is drawn from a population of size N by SRSWOR method. Then the standard error of sample mean will be zero if n is

Which type of sampling is one where only the first sample unit is selected at random and the remaining units are automatically selected in a definite
sequence at equal spacing from one another. It is :

In SRSWOR of size n from a population with N units if p is the proportion of sampled units having a given attribute, then unbiased estimate of V(p) is

When the collected data is grouped with reference to time, we have