S.R.S. Simple random sampling is the technique in which sample is so drawn that each and every unit in the population has an equal and independent chance of being included in the sample.
If the unit selected in any draw is not replaced in the population before making the next draw, then it is known as simple random sampling without replacement and if it is replaced back before making the next draw, then the sampling plan is called simple random sampling with replacement. Thus, simple random sampling with replacement always amounts to sampling from an infinite population, even though the population is finite.