Fractions are a little different, you can't simply add up numerators and denominators because fractions represent portions of something. Like a decimal.
To add up fractions you need to have a common denominator. This means converting the top and bottom numbers of ALL fractions to have the same bottom number. Then you can add them all up. From there you can average them.
25/50 + 17/20 + 13/20 -> 50/100 + 85/100 + 65/100 -> 50% ,85%, 65%.
(50 + 85 + 65) /3 = = 66%