Because of the increasing nuisance of spam e-mail messages, many start-up companies have emerged to develop e-mail filters. One such filter was recently advertised as being 95% accurate. This could mean one of four things.
(a)95% of the email allowed through is valid,
(b)95% of spam is blocked,
(c) of the blocked e-mail is spam, or
(d) 95% of valid e-mail is allowed through