Since, there are 6 science fiction stories, 4 adventure stories, 3 historical stories and 2 sport stories.
So, total number of stories = 6+4+3+2 = 15 stories
Probability that Artie selects a science fiction story =

Probability that Artie selects an adventure story =

Probability that story selected is either a science fiction or adventure fiction = P(Science) + P(Adventure)
=

=

= 0.66
=0.67
Therefore, the probability that the story Artie selects is either a science fiction story or an adventure story is 0.67.