In two experiments, participants judged the average numerosity between two sequentially presented dot patterns to perform an approximate arithmetic task. In Experiment 1, the response was given on a 0-20 numerical scale (categorical scaling), and in Experiment 2, the response was given by the production of a dot pattern of the desired numerosity (numerosity production). The experiments found that the responses were shaped according to an averaging integration model. This suggests the linearity in the response scale of both of the response methods in the approximate arithmetic task.