The Web site of a photo processor allows customers to send digital files of pictures to be printed on high-quality paper with durable inks. When the inks used by the processor start to run out, the color mix in the pictures gradually degrades.
(a) How could the facility use a quality control process to identify when it needed to switch ink cartridges? Will it be necessary to check every photo or only a sample of photos?
(b) If the facility samples photos, would it do better to group the photos into a large batch and then calculate a mean and standard deviation (for the measured color mix) or only wait a little while before calculating the mean and SD?