Tessa used 24mins of an 80min CD What percent of the CD has not been used? How many minutes is that?

70%, or 56 minutes. This can be calculated simply. You divide both 24 and 80 by 10, yielding 3 and 10, which we convert to the fraction 3/10. 3/10 is equivalent to 30%, and 100%-30%=70%. WE get the number of unused minutes with the following equation, 7/10*80=56