After spending some time studying company e-mail accounts, the manager of computer security for a large insurance company has determined that 25% of all e-mail messages sent to employee computers are spam.

If 80% of all spam e-mails sent to personal accounts contain the word guarantee in the Subject line, and only 4% of nonspam e-mails contain the word guarantee, what is the probability that an employee’s next e-mail that contains the word guarantee in the Subject line is spam?