In laboratory work it is desirable to run careful checks on the variability of readings produced on standard samples. In a study of the amount of calcium in drinking water undertaken as part of a water quality assessment, the same standard was run through the laboratory six times at random intervals. The six readings, in parts per million, were 9.54, 9.61, 9.32, 9.48, 9.70, 9.26. Estimate σ^2, the population variance for readings on this standard, in a 90% con dence interval. What assumptions did you make in calculating this confidence interval?