You ate more of the pie, the reason this is the case is because you ate 1.5 fourths of the pie. In order to solve these types of problems, you need to make the divisors of the amount of the pie you ate the same. in order to do this, we need to make 8 become 4, to do this we need to divide 8 by 2 which gives us four, remember what you do to the top of the fraction you MUST do to the bottom, which means that we need to divide the bottom by 2 which gives us 1.5.
We could also make the divisor of the fraction that expresses the amount of pie your sister ate 8 instead of making the other divisor 4. In order to do this, we must multiply 4 by 2 to give us 8, remember what we do to the top of the fraction you MUST do to the bottom, so we multiply the bottom by 2 giving us 2/8. You ate 1.5/4 and your sister ate 1/4 or your sister ate 2/8 and you ate 3/8. You ate more of the pie. I hope that this helped you out.