A precision instrument is guaranteed to read accurately to within 2 units. A sample of four instrument readings on the same object yielded the measurements 353, 351, 351, and 355. a. Find a 95% confidence interval for the population variance o' and also for the population standard deviation o. b. What assumptions are necessary? Does the guarantee seem reasonable? c. In this case, how can you obtain narrow confidence interval estimates for the vari- ance and standard deviation parameters