A baker must monitor the temperature at which cookies are ba

A baker must monitor the temperature at which cookies are baked. Too much variation will cause inconsistency in the texture of the cookies. Past records show that the variance of the temperatures has been 1.44 degrees. A random sample of 30 batches of cookies is selected, and the sample variance of the temperature is 4.41 degrees. Test the hypothesis that the temperature variance has increased above 1.44 degrees at = .05.

Solution

Ho: o^2=1.44
Ha: o^2 > 1.44
The test statistic is
Chisquare =(n-1)*s^2/o^2
=29*4.41/1.44
= 88.8125
Given a=0.05, the critical value of chisquare with df=n-1=29 is 41.34 (from chisquare table)
Since 88.8125 is greater than 41.34, we reject Ho.
So we can conclude that the variance in the number is increased than 1.44