The number of comic books that females like is 30/100*300=<<30/100*300=90>>90 books
Together, both males and females like 90+120=<<90+120=210>>210 comic books.
The number of comic books that are disliked by both males and females is 300-210=<<300-210=90>>90
The percentage of books that are disliked by both genders is 90/300*100=<<90/300*100=30>>30%
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