Without calculating values of z, tell which of these sample means will have the most extreme standardized score and which will have the least extreme standardized score.
40, 30, 25, 20.
Data lacking.
Without knowing population mean, standard deviation and sample size, it is impossible to know.
Z = (mean1 - mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√n
If only one SD is provided, you can use just that to determine SEdiff.
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to each Z score.