Boris has 20 CDs in his music collection. If 20% of the CDs are rock music and 60% of the CDs are pop music, how many CDs are other types of music?

20 CDs total
20% are rock
60% are pop
20 + 60 = 80
100-80=20
Other = 20%
20% of 20 = 4
So, Other = 20% = 4 CD’s