A Manufacturer Wants to Increase the Shelf Life of a Line

Multiple Choice

A manufacturer wants to increase the shelf life of a line of cake mixes. Past records indicate that the average shelf life of the mix is 216 days. After a revised mix has been developed,a sample of nine boxes of cake mix gave these shelf lives (in days) : 215,217,218,219,216,217,217,218,and 218. Using α = 0.025,has the shelf life of the cake mix increased?

A) Yes,because computed t is greater than the critical value.
B) Yes,because computed t is less than the critical value.
C) No,because computed t lies in the region of acceptance.
D) No,because 217.24 is quite close to 216.