Question

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.

Answer 1

Answer:

a. no, there are no sufficient data to use

b. assumption b is right

Step-by-step explanation:

a. for the standard deviation to be calculated at 99% confidence, the data needed should be the mean (given), the variate value to be calculated for(not given), the standard deviation(not given), the z value of the normal distribution ( not given),

since there are too many unknown, the data given are not sufficient to calculate.

b. validity of this interval requires that coating layer thickness be at least approximately normally distributed.