The percentage of 24 songs to 78 songs is really 30.7692308%, but, rounded, it is really 30%.
°°°How to get the answer?
It's pretty simple. Just think of 24 songs to 78 songs as a fraction. Divide the numerator by the denominator, and then multiply by 100 to get your answer.
Simple, right?
↑ ↑ ↑ Hope this helps! :D