Wire electrical-discharge machining (WEDM) is a process used to manufacture conductive hard metal components. It uses a continuously moving wire that serves as an electrode. Coating on the wire electrode allows for cooling of the wire electrode core and provides an improved cutting performance. An article gave the following sample observations on total coating layer thickness (in um) of eight wire electrodes used for WEDM 21 17 29 36 42 24 25 25.
Calculate a 99% CI for the standard deviation of the coating layer thickness distribution. (Round your answers to two decimal places.) Is this interval valid whatever the nature of the distribution? Explain.
a. Yes, there are enough data points for this interval to be valid.
b. No,validity of this interval requires that coating layer thickness be, at least approximately, normally distributed.