Boris has 20 Cd's in his music collection. Given that 20% of the CD's are rock music and 60% of them are pop music. How many CD's are other types of music.
The total amount of CD's are 100% so 100 - (20+60) = 20% -> the percentage of the other types of music. Then multiply 20% by 20 to get 4. So there are 4 CD's that are other types of music
