Plastic sheets produced by the machine are periodically monitored for the possible fluctuations in thickness. If true variance in thickness exceeds 2.25 square millimeters, there is cause for the concern regarding product quality. Thickness measurements for random sample of 10 sheets produced in a specific shift were taken, given the following results:
226, 226, 232, 227, 225, 228, 225, 228, 229, 230
Test at the 5% significance level the null hypothesis that population variance is at most 2.25