Having developed a construction technique for confidence intervals for mean with σ known, we now drop our simplifying assumption and address the common case when we do not know much about the populat...Having developed a construction technique for confidence intervals for mean with σ known, we now drop our simplifying assumption and address the common case when we do not know much about the population; i.e. we do not know the population mean or population standard deviation. We must know that the sampling distribution of sample means has either a normal parent population or the sample size n is greater than 30. Now we create our confidence intervals when population parameters are unknown.