Plastic sheets produced by a machine are periodically monitored for possible fluctuations in thickness. If the true variance exceeds 1.65 square millimeters, there is cause for concern about product quality. Thickness measurements for a random sample of 10 sheets produced in a particular shift were taken, giving the results shown below (in millimeters). 229 230 230 225 227 229 226 228 229 a. Find the sample variance. 229 b. Test, at the 5% significance level, the null hypothesis that the population variance is at most 1.65 square millimeters. Click the icon to view the upper critical values of Chi-square distribution table.