Question 1191438: 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, 219, 217, 220 and 218. At the 0.025 level, has the shelf life of the cake mix increased?
A. No, because computed t lies in the region of acceptance.
B. No, because 217.24 is quite close to 216.
C. Yes, because computed t is greater than the critical value.
D. Yes, because computed t is less than the critical value.
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! mean is 217.67
s=1.58
assuming sd of sample is unbiased estimator of pop.
use 1 way test here if expected to increase. Critical value is t>2.306
t=(217.67-216)/1.58/sqrt(9)
=1.67*3/1.58
=3.17
Yes, because computed t is > critical value
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