The maximal margin of error when constructing a 95 CI for a

The maximal margin of error when constructing a 95% CI for a normal population mean was 0.5 from sample size 200. How many observations are necessary to make the maximal margin of error 0.25 at the same confidence level?

Solution

To make margin of error half, we need to quadruple the sample size, i.e, 200*4 = 800