What does (Sample Means) mean??... Does it mean the averages of many samples ??..If yes, how does he say that we need at least 30 observations to apply CLT, that is only 1 sample!!

Hey Anas, Yes, your intuition is correct. In this case, to obtain a normal distribution you need at least 30 random samples. Each of these samples will have a sample mean. Best, Ned

I thought that it means that one observation = 1 sample. The mean of a sample of 1 is itself. We can assume CTL if the number of observations is >= 30, i.e. n = 30. If it's the mean of 30+ samples where each sample can be more than 1 observation, then that will give a more accurate result but I think the min requiremement is 30, single samples from a single population.