What is the rationale for using the coefficient of variation $c$ instead of the standard deviation

$$ as a measure of variability?

For the following random variables, indicate whether you would expect each to be LV$,$ MV$,$ or

HV$.$

$($a$)$ Time to complete this set of study questions

$($b$)$ Time for a mechanic to replace a muffler on an automobile

$($c$)$ Number of rolls of a pair of dice between rolls of seven

$($d$)$ Time until failure of a machine recently repaired by a good maintenance technician

$($e$)$ Time until failure of a machine recently repaired by a not$-$so$-$good technician

$($f$)$ Number of words between typographical errors in the book Factory Physics

$($g$)$ Time between customer arrivals to an automatic teller machine