The population standard deviation of strengths of steel bars produced by a large manufacturer is 2.95. In order to meet tighter specifications engineers are trying to reduce the variability of the...

The population standard deviation of strengths of steel bars produced by a large manufacturer is 2.95. In order to meet tighter specifications engineers are trying to reduce the variability of the process. A sample of 28 bars gives a sample standard deviation of 2.65. Assume that the strengths of steel bars are normally distributed. Is there evidence at the 5% level of significance that the standard deviation has decreased?