$2.$ The mean time to expose a single panel in a circuit$-$board plant is two minutes with a standard deviation of $1\mathrm{.}5$ minutes.

a$.$ What is the natural coefficient of variation?

b$.$ If the times remain independent, what will be the mean and variance of a job of $60$ panels? What will be the coefficient of variation of the job of $60?$

c$.$ Now suppose times to failure on the expose machine are exponentially distributed with a mean of $60$ hours and the repair time is also exponentially distributed with a mean of two hours. What are the effective mean and CV of the process time for a job of $60$ panels?