Thread: Sampling Distributions

If the systolic blood presure for a certain group of obese people has a mean of 132 and a standard deviation of 8. If we take sample of 100 poeple from the population, what is the probability that the group has an average systolic pressure above 128?

My answer to this problem is :
n=100, X bar~N(132,8/√100) -> X bar~N (132, .80)

P(X bar > 128) = ?? -> Z=(128-132) / .80=-.50?????

.50 couldn't be the Z value. Am i done something wrong??

Please HELP~~

-4 divided by 4/5?