Question

The mean weight of 25 female is 115 lb. with a standard deviation of 10 lb. What is the standard error of the mean weight? What is the 95% confidence interval for the mean? Show all your computations.

Answer 1

solution:

sample size = n = 25

sample mean = = 115 lb

sample standard deviation = S = 10 lb.

standard error

confidence level = 95% = 0.95

so, = 1 - 0.95 = 0.05

since population standard deviation is not known so we use t distribution

degree of freedom =df = n - 1 = 25 - 1 = 24

critical value of t =

margin of error

confidence interval =

upper limit = 115 + 4.128 = 119.128

lower limit = 115 - 4.128 = 110.872

so, confidence interval = (110.872, 119.128)