Detailed Instructions: The task is to generate the correct answer for a given math problem.
Problem:Problem: in a park there are two ponds with both brown ducks and green ducks . in the smaller pond there are 45 ducks and in the larger pond there are 55 ducks . if 20 % of the ducks in the smaller pond are green and 40 % of the ducks in the larger pond are green , then what percentage of ducks are green ?
Solution:
31 %