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.
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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.
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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.
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Fig. 19.
There were now thirty-six boys sleeping in the dormitories, and next
night they were joined by four more, which brought the number up to
forty, and yet the master only counted twelve in each dormitory on his
rounds that night. How the new distribution was made is shown in Fig.
20.
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Fig. 20.
Next night four more chums popped in for a snooze, making a total of
forty-four, and again the master was bamboozled by the following
readjustment (Fig. 21).
[Illustration]
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Fig. 21.
History is silent upon the subject of the arrangement at the
breakfast-tables.
The proper way to present this puzzle to your friends is to lay
forty-four matches on the table, and after showing the initial
arrangement, allow them to work the rest out for themselves.