This study examines how problem solvers use distributing working memory resources over internal and external epresentations. Participants played three-dimensional versions of number guessing games. The playing of number guessing games is directly related to consumption of working memory resources. They could use arbitrarily the game record windows which are the external representations of these games and, thus, they could distribute working memory demands over internal working memory resources and external representations. The extents of their using external representations differed depending on the participants. The participants (8 students) who used the external representations on all 10 games did better performances than the participants (43 students) who used the external representations on several games not on all games and the participants (19 students) who did not use the external representations, and got more game record windows than 43 participants who used the external representations not on all 10 games. The results provide evidence about the roles of the external representations and individual differences on the extents of using the external representations.