ABSTRACT
We asked each child to write down on a piece of paper an initial number n (without announcing it), add 3 to it, then multiply the result by 2 and, finally, add 5. Thus the final result n' = 2 (n + 3) + 5. The problem was to judge whether the experimenter, who had his back turned and therefore had no idea what n was, could reconstruct this initial number once informed about the final number n'. Naturally, what is most important is establishing how the child, whether or not he thinks this reconstruction is possible, would explain it in terms of the inversion of the arithmetic operations that were being carried out.
