Damian recorded the grade-level and instrument of everyone in the middle school School of Rock below.
Seventh Grade Students
Instrument # of Students
Guitar 13
Bass 4
Drums 11
Keyboard 5
Eighth Grade Students
Instrument # of Students
Guitar 5
Bass 3
Drums 8
Keyboard 11
Based on these results, express the probability that a student chosen at random will play an instrument other than guitar as a fraction in simplest form.
