Fig. 16.
THE ARTFUL SCHOOLBOYS
At a certain school were four long dormitories, built in the form of a square, in which thirty-two boys occupied beds, as shown by matches in [Fig. 17].
Fig. 17.
By this arrangement the master, in going his rounds at night, counted twelve boys in each corridor. One night four boys absented themselves from the school, and the remaining boys rearranged themselves in such a manner that the master was still able to count twelve boys in each corridor, and the absence of their four comrades was not noticed. How they did it is shown in [Fig. 18].
Fig. 18.
The four absentees returned on the following night, accompanied by four friends; but the master was unable to notice the addition, for he again counted twelve boys in each dormitory. The new arrangement was as [Fig. 19].