I just taught the children this question. The answer is: 1 chicken and 1 duck, 1 duck is heavier. The thinking process is like this: only consider their average weight, that is, each duck has the same weight and each chicken has the same weight. The weight of a goose is equivalent to the weight of two ducks, so the weight of two geese is equivalent to the weight of four ducks. As can be seen from the right figure, if the weight of two geese is greater than that of four chickens, it can be concluded that the weight of four ducks is greater than that of four chickens, so the average weight of each duck is greater than that of each chicken, so 1 duck is heavier.