The entirety of 8 ducks as a fraction is 8/8.
So 2 ducks have blue wings which means that represents a quarter (25%) of the total ducks.
A quarter as fraction is 1/4.
Ex to understand de logic:
1/1 is a full (100%)
1/2 is a half (50%)
1/4 is a quarter (25%)
In our case 8/8 equals with 1/1 (100% of the ducks).