Answer with explanation:
He has 20 rock songs, 15 country songs, 10 world songs and 5 classical songs. 
There are 50 in total.
- The fraction of songs which are rock songs are:
 
 
 
which in simplest fraction is given by:
 

and on multiplying the fraction with 100 we get the percent of songs.
Hence,

- The fraction of songs which are country songs are:
 
 
 
which in simplest fraction is given by:
 

Hence,

- The fraction of songs which are world songs are:
 
 
 
which in simplest fraction is given by:
 

Hence,

- The fraction of songs which are classical songs are:
 
 
 
which in simplest fraction is given by:
 

Hence,
