Hello there. To solve this question, we'll have to calculate the percentage of which rock musics represents of the amount of music Carl has in his MP3 player.
Knowing he have 200 songs on his MP3 player and 25 of these are rock, to find this percentage, we calculate the ratio between how many are rock and the sample size:
25/200
Simplify the fraction by a factor of 2
12.5/100
This means that it represents 12.5%.