3. For a 95% confidence level, find the z-critical value. To do this, click in an empty cell and type
=NORMSINV(0.975). (We use 0.975 because, a = .05. Since we are working with a confidence
interval, we divide a by 2. Therefore we get .05/2 = .025. The normsinv uses the area to the
left of the positive critical value, which gives us 1- .025 = .975.)
critical value z =
