Mario ordered a pizza for dinner when it arrived, mario quickly ate 1/8 of the pizza. while mario went to go get napkins. his pet poodle ate 1/3
a.) write a numerical expression to show the fraction of the pizza that is left

The first thing to do is to make the denominators the same: 
1 X 3 = 3.  8 X 3 = 24
1 X 8 = 8.  3 X 8 = 24

3/24 + 8/24 = 11/24

The whole pizza is 1.  The one can be written as a fraction: 
1/1

1 X 24 = 24

24/24 - 11/24 = 13/24

24/24 - (3/24 + 8/24) = 13/24

A: 0.26 would be the answer