According to the conditions, in the strict sense in which one at first
understands them, there is no possible solution to this puzzle. In such
a dilemma one always has to look for some verbal quibble or trick. If
the owner of house A will allow the water company to run their pipe for
house C through his property (and we are not bound to assume that he
would object), then the difficulty is got over, as shown in our
illustration. It will be seen that the dotted line from W to C passes
through house A, but no pipe ever crosses another pipe.
252.--A PUZZLE FOR MOTORISTS.
[Illustration]
The routes taken by the eight drivers are shown in the illustration,
where the dotted line roads are omitted to make the paths clearer to the
eye.
253.--A BANK HOLIDAY PUZZLE.
The simplest way is to write in the number of routes to all the towns in
this manner. Put a 1 on all the towns in the top row and in the first
column. Then the number of routes to any town will be the sum of the
routes to the town immediately above and to the town immediately to the
left. Thus the routes in the second row will be 1, 2, 3, 4, 5, 6, etc.,
in the third row, 1, 3, 6, 10, 15, 21, etc.; and so on with the other
rows. It will then be seen that the only town to which there are exactly
1,365 different routes is the twelfth town in the fifth row--the one
immediately over the letter E. This town was therefore the cyclist's
destination.
The general formula for the number of routes from one corner to the
corner diagonally opposite on any such rectangular reticulated
arrangement, under the conditions as to direction, is (m+n)!/m!n!,
where m is the number of towns on one side, less one, and n the number
on the other side, less one. Our solution involves the case where
there are 12 towns by 5. Therefore m = 11 and n = 4. Then the formula
gives us the answer 1,365 as above.
254.-- THE MOTOR-CAR TOUR.
First of all I will ask the reader to compare the original square
diagram with the circular one shown in Figs. 1, 2, and 3 below. If for
the moment we ignore the shading (the purpose of which I shall proceed
to explain), we find that the circular diagram in each case is merely a
simplification of the original square one--that is, the roads from A
lead to B, E, and M in both cases, the roads from L (London) lead to I,
K, and S, and so on. The form below, being circular and symmetrical,
answers my purpose better in applying a mechanical solution, and I
therefore adopt it without altering in any way the conditions of the
puzzle. If such a question as distances from town to town came into the
problem, the new diagrams might require the addition of numbers to
indicate these distances, or they might conceivably not be at all
practicable.
[Illustration: Figs. 1, 2, and 3]
Public-domain text, read in full here on John Shaqi.
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