A computer-supply retailer purchased a batch of 1,000 CD-R disks and attempted to for-mat them for a

Question:

A computer-supply retailer purchased a batch of 1,000 CD-R disks and attempted to for-mat them for a particular application. There were 857 perfect CDs, 112 CDs were usable but had bad sectors, and the remainder could not be used at all.
a. What is the probability a randomly chosen CD is not perfect?
b. If the disk is not perfect, what is the probability it cannot be used at all?

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