Question 1136580
population mean is loss of 40 pounds on the average.
population standard deviation is plus or minus 12 pounds on the average.


sample size is 36.


standard deviation of sample means is 12 / sqrt(36) = 12 / 6 = 2


z-score for this sample of 36 dieters is (45 - 40) / 2 = 5/2 = 2.5.


the z-score formula is z = (x-m)/s


z is the z-score
x is the sample mean.
m is the population mean.
s is the standard deviation of the distribution of sample means.


formula for standard deviation of sample means is s = standard deviation of the population divided by the square root of the sample size.