A cement manufacturer claims that concrete prepared from his product has a relatively stable compressive strength and that the strength measured in kilograms per square centimeter (kg/cm2) has a variability of 10 kg/cm2 or less. A sample of n = 10 measurements produced a mean and variance equal to 312and 195, respectively.
A) Construct 90% confidence interval for the variance.
B) Do these data present sufficient evidence to reject the manufacturer's claim?