Thread: Sample mean

A new paper calls 20 of its subscribers to determine their mean income. The distribution of the sample mean is:

a. unknown
b. binomial
c. normal
d. approximately normal


A sample of 25 is taken from a population which has a normal distribution with a mean of 60 and standard deviation of 15. The probability that the sample mean is between 55.5 and 64.5 is:

a. .0668
b. .2668
c. .5468
d. .8664
e. .9332


Decreasing the sample size:

a. decrease the sample mean
b. decrease the standard deviation of the sample mean
c. increase the standard deviation of the sample mean
d. increase the sample mean

the answer to your third problem is: c