Maria and jane bought a whole pizza pie. marie ate 1/5 of the pie and jane ate 1/4 of the pie. write a number sentence to find out how much is left and solve it

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