Why 90% of rar and zip files cant be opened?

Well i have an android and it seems that this is the problem cause i don't have a computer and I've tried to unrar and unzip a lot of files like roms and 90% of the time It ends in an error no matter what I've done I've tried androzip the app, but nothing the same error or can't be opened. Is... show more Well i have an android and it seems that this is the problem cause i don't have a computer and I've tried to unrar and unzip a lot of files like roms and 90% of the time It ends in an error no matter what I've done I've tried androzip the app, but nothing the same error or can't be opened. Is there other way to unpack a rar or zip file???
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