Answer: 9 CDs are other types of music.
Yes , you can add 40% and 30% to get the percentage of CDs that are country music or pop music.
Explanation:
Given : Harrison has 30 CDs in his music collection.
Percentage of CDs are country music = 40%
Percentage of CDs are pop music= 30%
We will add 40% and 30% to get the percentage of CDs that are country music or pop music.
Percentage of CDs that are country music or pop music = 40% +30% = 70%
Percentage of other types of CDs = 100%-Percentage of country music or pop music
=100%-70%=30%
Now, the number of other types of CDs = Percentage of other types of CDs x Total CDs
=30% of 30 =

Hence, 9 CDs are other types of music.