"
Four men crossing a bridge" is a
logic puzzle that I
came across a few years
ago. I particularly
enjoy this puzzle because it
appears simple at
first glance but becomes
deviously complex as you
attempt to
solve it. I did not
make it up, and take no
credit for it's
invention. Unfortunately, I am
unaware of it's
origin.
Four men are travelling through a
forest when they come upon a
rickety old
bridge spanning a gaping
chasm. The bridge can only
hold the
weight of two men at once, and it is so
dark that a flashlight is
necessary to successfully
navigate. Since the men only have one
flashlight among them, they will keep sending two men
across the bridge and have one bring the light
back until
all four are across. The four men are of
different physical ability, and they can cross the bridge in one minute, two minutes, five minutes and ten minutes
respectively. If two men cross the bridge, they must both travel the
speed of the
slower man. For example, if the
one minute man and the ten minute man travel across together, it will take them both ten minutes to get across. What is the fastest time all four can successfully
cross the bridge?
Although
lateral thinking is a
good thing, it is not used to
solve this puzzle (i.e. the men do not use the flashlight to
signal a
helicopter to take all four across in one minute.) There are no
word tricks here, just try to figure out the most
efficient use of each man's ability to
span the bridge. Feel
free to add your own
solutions to this
node, and we'll
see who can come up with the
fastest time.