The mean time to expose a single panel in a circuit-board plant is two minutes with a

standard deviation of 1.5 minutes.

a. What is the natural coef cient 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 coef cient 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?

standard deviation of 1.5 minutes.

a. What is the natural coef cient 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 coef cient 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?

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