CROSSING THE STREAM.
(
Measuring, Weight, and Packing Puzzles.)
During a country ramble Mr. and Mrs. Softleigh found themselves in a
pretty little dilemma. They had to cross a stream in a small boat which
was capable of carrying only 150 lbs. weight. But Mr. Softleigh and his
wife each weighed exactly 150 lbs., and each of their sons weighed 75
lbs. And then there was the dog, who could not be induced on any terms
to swim. On the principle of "ladies first," they at once sent Mrs.
Softleigh over; but this was a stupid oversight, because she had to come
back again with the boat, so nothing was gained by that operation. How
did they all succeed in getting across? The reader will find it much
easier than the Softleigh family did, for their greatest enemy could not
have truthfully called them a brilliant quartette--while the dog was a
perfect fool.
374--CROSSING THE RIVER AXE.
Many years ago, in the days of the smuggler known as "Rob Roy of the
West," a piratical band buried on the coast of South Devon a quantity of
treasure which was, of course, abandoned by them in the usual
inexplicable way. Some time afterwards its whereabouts was discovered by
three countrymen, who visited the spot one night and divided the spoil
between them, Giles taking treasure to the value of L800, Jasper L500
worth, and Timothy L300 worth. In returning they had to cross the river
Axe at a point where they had left a small boat in readiness. Here,
however, was a difficulty they had not anticipated. The boat would only
carry two men, or one man and a sack, and they had so little confidence
in one another that no person could be left alone on the land or in the
boat with more than his share of the spoil, though two persons (being a
check on each other) might be left with more than their shares. The
puzzle is to show how they got over the river in the fewest possible
crossings, taking their treasure with them. No tricks, such as ropes,
"flying bridges," currents, swimming, or similar dodges, may be
employed.
Answer:
First, the two sons cross, and one returns Then the man crosses and the
other son returns. Then both sons cross and one returns. Then the lady
crosses and the other son returns Then the two sons cross and one of
them returns for the dog. Eleven crossings in all.
It would appear that no general rule can be given for solving these
river-crossing puzzles. A formula can be found for a particular case
(say on No. 375 or 376) that would apply to any number of individuals
under the restricted conditions; but it is not of much use, for some
little added stipulation will entirely upset it. As in the case of the
measuring puzzles, we generally have to rely on individual ingenuity.
