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Conditional Probability: Testing Software

ALGEBR-TKG9TE

Mac-fee Software Company tests software for viruses with the following results:

(1) For software that really has a virus, the test says ``Yes" 99% of the time;

(2) For software that is really is virus-free, the test says ``Yes" 1% of the time.

If 1% of all software has a virus, what are the chances that the software really has a virus and the test says ``Yes"?

A

0.0099

B

0.0999

C

0.0001

D

0.0010