math
posted by caintgetrite .
for a sample of n = 75, find the probaBILITY OF A SAMPLE MEAN BEING BEIGN GREATER THAN 221 IF U = 220 AND O = 3.9

First, please do not use all capitals. Online it is like SHOUTING. Not only is it rude, but it is harder to understand. Thank you.
I assume "U" = mean and "O" = standard deviation.
Z = (mean1  mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√(n1)
Since 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 related to that Z score.