So theres 4 hours and 60min equals 1 hour, so multiply 4 by 60 to get 240, so theres 240 minutes of time on the mp3. So 1/6 of that total time (240min) was on jazz, so what you do is divide 240 by 6 to get 40, so every 1/6 is 40min. So you could say he spend 40min listening to jazz, or you could say he spent 2/3 of an hour listening to jazz
