Y=-1/4x+7.5 is the right equation
Answer:
The normality requirement for a confidence interval estimate of sigma is (stricter) than the normality requirement for a confidence interval estimate of mu. Departures from normality have a (greater) effect on confidence interval estimates of sigma than on confidence interval estimates of mu. That is, a confidence interval estimate of sigma is (less)
As the width gets larger so does the total area
They need to have common denomenators so change the fractions to 12/15 - 5/15 which is 7/15.