The standard error of the mean for sample of 100 is 30 In or

The standard error of the mean for sample of 100 is 30. In order to cut the standard error of the mean to 15. We would decrease the sample size to 50 increase the sample size to 200 increase the sample size to 400 decrease the sample to 25

Solution

to make margin of error half, we need to quadruple the sample size because of formula: ME = std * z / (sqrt(n))

Option (C) is correct