This little jest on the part of Major Trenchard is
and the face of the roguish boy on the extreme right, with
the figure 9
on his back, showed clearly that he was in the secret, whatever that
secret might be.
I have no doubt (bearing in mind the Major's hint as
the numbers being "properly regarded") that his answer was that
in the illustration, where boy No. 9 stands on his head and so converts
his number into 6.
This makes the total 36—an even
number—and by making
boys 3 and 4 change places with 7 and 8, we get 1278 and 5346, the
figures of which, in each case, add up to 18.
There are just three
ways in which the boys may be grouped: 1368—2457,