just realized this is an old question
One dozen eggs is 48 eggs. Altogether that costs 40 dollars. If six of the eggs were broken then the money wasted would be 5 dollars.
The reason that it is 5 dollars is becuase it takes 10 to buy 12 eggs, and half of that is 6. So divide both 12 and 10 (separately) and you get 5 dollars for 6 eggs.
To get the percent you must divide 5 by 40.
The answer comes out to about 12.5% or 0.125.
So in the end, 12.5% of the money was wasted due to the broken eggs.
Hope this helped!