2. An astronomer is measuring the distance to a star. Because of measurement errors, each measurement will not be precisely correct, but merely an

This is the answer key to a practice test. I am having trouble understanding that answer. What are the Z's? Is 4 supposed to be the SD rather than the SE? Thanks.

2. An astronomer is measuring the distance to a star. Because of measurement errors, each measurement willnot be precisely correct, but merely an estimate. She will therefore make a series of measurements and usethe average as her estimate of the distance. She believes her measurements are independent and identicallydistributed with mean d light years and SE of 4 light years. How many measurements does she need to make to be 95% sure her estimate is accurate to within 0.5 light-years? in?)1. n;A