There are four people
who want to cross a bridge; they all
begin on the same side. You have 17 minutes to get them all across to
the other side. It is night, and they
have one flashlight. A maximum of two people
can cross the bridge at one time. Any party that crosses, either one or
two people, must have the flashlight with them. The flashlight must be
walked back and forth; it cannot be
thrown, for example.
Person 1 takes 1
minute to cross the bridge, person 2 takes 2 minutes, person 3 takes 5
minutes, and person 4 takes 10 minutes.
A pair must walk together at the rate
of the slower person’s pace. For example, if person 1 and person 4
walk across first, 10 minutes have
elapsed when they get to the other side of
the bridge. If person 4 returns the flashlight, a total of 20 minutes
have passed and you have failed
the mission.

**Solutions:**

Let 1, 2, 5, 10
be labels representing the men of the problem, f
represent the
flashlight’s location, and the number in the parenthesis be the total
amount of time elapsed. The following sequence
of moves solves the problem:

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Solutions