Amanufacturer 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 less than the critical value.
b. yes, because computed t is greater 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.