The mean would be the result of (25 + 30 + 35 + 20) / 4 or 27.5 rounded to 28. To find the variance, first find the difference between the mean and each set of data.

Since the T-Value is a comparison between sample mean and population mean, both values need to be available in order for you to calculate the T-Value.

For estimating the mean of a finite population using information on an auxiliary variable, a class of estimators is defined as a function of the ratio of sample mean to population mean and the ratio ...

Estimates of Mean Population Denisty and Spatial Distribution of Tetranychus urticae (Acarina: Tetranychidae) and Phytoseiulus persmilis (Acarina: Phytoseiidae) Based Upon the Proportion of Empty ...