According to Tchebysheff's theorem what % of measurements must lie within 2.5 standard deviations of the mean?

The existence of a quality control manual at your key supplier means

An X-bar chart has shown control for a long time. You see that points for the last 50 samples are all very near the center line on the chart. In fact, they are all within one sigma of the center line. This probably indicates that

The difference between setting alpha equal to 0.05 and alpha equal to 0.01 in hypothesis testing is

Compute the upper control limit for an s chart, based on a sample size of 10, if the process is in control with a mean of 40 and a sample standard deviation of 7.