Eleven Twentieths of the pie are left, so that's 11/20
Method to solve; Since its given a 1/4 and a 1/5 it's easiest to convert these to twentieths (the lowest common multiple of 4 and 5) So 1/4= 5/20 1/5 = 4/20 How much is eaten = 5/20 + 4/20 = 9/20 How much remains = Total (20/20) - How much eaten (9/20) = 11/20