Final answer:
The symbol Σ in formulas for means represents the operation of summing all observations in a data set.
Step-by-step explanation:
In the formula for the sample mean or for the population mean, the symbol Σ (Greek capital letter sigma) represents the operation of summing all observations.
For example, if you have a data set of numbers, summing these numbers together would involve adding each of them up to get a total. This total is then typically divided by the number of observations to calculate the mean.
The Σ symbol specifically signifies that you should add up all the values in the data set. It does not represent all observations by themselves (as just a collection), the total number of observations (which would be the count of all values), or any operation but specifically the summation operation.
The symbol μ represents the population mean and it is a parameter. In order for the sample mean to be a good estimate of the population mean, the sample needs to be truly random.